autoplast of the chlorophyll-grains consists of a light-coloured matrix in which are imbedded green grains. The phenomena of swelling and other reactions are explained by the following hypothesis :-Every grain contains an invisible inclosed substance soluble in water; the solution of this stretches the framework, which swells at the same time, and which forms a relatively dense envelope around the inclosed substance. The oily substances inclosed, he determined not to consist of a fixed (fatty) oil.

In the passage of autoplasts into anaplasts and chromoplasts, chemical and morphological differences are observable. The former are shown by the different behaviour towards reagents; the latter consist of a change in the structure, size, and mass of the trophoplast.

The form of the trophoplast is altered first of all by foreign bodies which grow in or on it. The autoplasts of many plants also undergo a change of form under the influence of rays of light. The position of the trophoplasts within the cells is also not fixed, light and gravitation causing variations in this respect.

From the investigation of starch-grains in parenchyma-cells of colourless stems, petals, fruits, seeds, and scales, the author draws the conclusion that wherever starch-grains occur, trophoplasts are also present, in or on which the starch-grains grow. The viridescence of ordinarily colourless parts of plants always depends on the transformation into autoplasts of anaplasts already present in the colourless cells. Wherever looked for, in parenchyma-cells, epidermal cells, sclerenchymatous cells, and sieve-tubes, the author always found trophoplasts.

In all cases where chlorophyll-grains are formed by the investment of starch-grains with viridescent protoplasm, the first stage is always the formation of trophoplasts. Observations on the development of the autoplasts of Allium Cepa and Elodea led to the conclusion that trophoplasts never arise from a differentiation of the protoplasm; but that they always multiply by division, and, with the protoplasm in which they are imbedded, always pass in a young and small condition into the daughter-cells on the division of a meristem-cell; there they increase further by division, grow with the cell either into anaplasts or into autoplasts and chromoplasts, and usually disappear with the death of the cell.

Mechanism of the Splitting of Legumes.*-According to C. Steinbrinck, the splitting of legumes is chiefly the result of hygroscopic tensions between the ligneous layer and the outer epidermis, alone or together with the hypoderm. These tensions are caused not only by the greater capacity of the ligneous layer for swelling, but depend essentially on the cross position of the cells of both tissues, which contract more in the transverse than in the longitudinal direction. This difference of contraction being greatest in the direction of the tangential transverse diameter of the ligneous fibres, these bring about a spiral curving inwards of both valves of the legume, which causes them eventually to spring asunder. In the different

*Ber. Deutsch. Bot. Gesell, i. (1883) pp. 270-5.

genera and species this curvature is more or less strengthened by the capacity for swelling of the masses of cellulose in the ligneous layer increasing more or less from the outside inwards.

Aerial Vegetative Organs of Orchidee in relation to their Habitat and Climate.*—An examination of the structure of a large number of both native and tropical Orchideæ leads P. Krüger to the following general conclusions on this subject:-Starting from the native species, there may be seen, both in the foliar and axial organs, a series of gradual variations, which increase in importance as the climatic conditions of the species vary from ours. In one group of tropical orchids the original herbaceous habit is still maintained; while contrivances to suit other conditions are perfected in changes in the parenchyma, having for their purpose the absorption of the water necessary for the plant, and protection from transpiration. In a further stage the herbaceous form is abandoned as unsuitable, and the succulent form assumed; while in a third type the development of a mechanically firm and resistant system strengthens the epidermal tissue, or assists in the formation of special receptacles for water, or a combination of the two means. All these changes are accompanied by corresponding changes in the cuticle, having for their object the diminution of transpiration in tropical orchids.

Assimilation of Carbonic Acid by Protoplasm which does not contain Chlorophyll.t-By experiments on Penicillium glaucum, J. Reinke finds that all the carbon-acids tested, with the exception of carbonic, formic, and oxalic acids, are of equal value for its nutrition, but are useful only when in combination with bases. The methyl-group can in many cases supply the fungus with carbon; as also can the group C, H. Before it becomes serviceable to the plant, the carbon of the acids must apparently enter into combination with hydrogen, in consequence of a process of reduction brought about by the assistance of water, and by means of protoplasm.

Artificial Influences on Internal Causes of Growth,+-E. Wollny points out that the reason why the secondary shoots of woody plants grow more rapidly when the main stem is decapitated, is not merely that they receive a better supply of nourishment, but that the conditions of the soil are altered through greater access of moisture and warmth. The popular idea that vegetation keeps the ground moist is exactly the reverse of the truth.

Absorption of Food by the Leaves of Drosera.§-By a series of experiments, M. Büsgen has confirmed in a very striking manner the observations of Rees and Darwin as to the capacity of Drosera rotundifolia for absorbing nutriment through the leaf. The number of inflorescences and capsules was found to average very much higher (from three to five times as many), when the leaves were fed with

* Flora, lxvi. (1883) pp. 435–43, 451-9, 467-77, 499-510, 515-24 (2 pls.). Reinke's Unters. Lab. Göttingen, Heft 3. See Bot. Ztg., xli. (1883) p. 551. Wollny's Forsch. Geb. Agrikulturphysik, vi. (1883) pp. 97-134. See Biol. Centralbl., iii. (1883) p. 385.

§ Bot. Ztg., xli. (1883) pp. 569-77, 585–94.

insects, compared with those not so fed under similar circumstances, even when an abundant supply of a nutrient fluid was furnished to their roots.

Mechanical Action of Light on Plants.*-F. Cohn has investigated not so much the cause of the apparently spontaneous movements of the lower plants and of animals, as the forces which induce those movements to assume certain definite directions.

Non-chlorophyllaceous organisms, such as monads and the zoospores of fungi, move freely in every direction indifferently in reference to the incidence of the rays of light.† Diatoms and Oscillariem, coloured respectively by phæophyll and phycochrome, always prefer light to darkness, and accumulate therefore on the surface of the water. When the field is equally illuminated in all directions, diatoms are distributed uniformly through the water, and Oscillarieæ radiate equally in all directions. Green microscopic organisms which contain chlorophyll, such as Euglencæ, Volvocineæ, and the zoospores of most algæ, always display a certain polarity, one end being destitute of chlorophyll and usually provided with cilia and a red "eye-spot," and being also more pointed in comparison to the other end, which is coloured a deep green. The pointed end is always the anterior end in the "swarming" motion; and this advancing motion is always accompanied by a rotating movement round the longitudinal axis which passes through the two ends; the direction of this rotation varies in different organisms. A number of experiments undertaken by Cohn show that when the direction of the incidence of the light on the field of view is made to vary, the direction of the motion of these green organisms varies with it; they always seek light and avoid darkBut it is a remarkable fact in connection with this, that it is the direction rather than the intensity of the light that seems to influence them; as is seen when the light is reflected on to the field of view from a mirror. Reflected light appears to have no more effect in influencing the direction of their movements than absolute darkness. Experiments with coloured glasses show that it is only the more refrangible actinic rays which have this effect on the movements of minute organisms; the less refrangible, which have no chemical action, have also no effect of this kind. A few exceptional organisms display a power of motion in the opposite to the ordinary direction.

ness.

A comparison of these movements with those of artificial euglenas which are made to evolve carbon dioxide from one end, shows that the direction of the movement is dependent on the decomposition of carbon dioxide by the aid of the organism which contains chlorophyll, and hence on its polarity.

These movements of green swarm-spores and similar bodies are compared by the author with the phototonic movements of the organs of plants, on which many observations have recently been made, especially by Stahl.‡

JB. Schles. Gesell. Vaterl. Cult., 1883, pp. 179–86.

With the exception, however, of bacteria, as shown by Engelmann. See this Journal, ii. (1882) pp. 380, 656; iii. (1883) p. 256. See this Journal, ii. (1882) p. 373.

Action of the Amount of Heat and of Maximum Temperature on the Opening of Flowers.*-W. von Vogel states, as the results of a series of experiments, that the maximum temperature of the day has seven times greater influence on the opening of flowers than the average daily temperature. The mode of obtaining this result is detailed in the paper.

Behaviour of Vegetable Tissues towards Gases.t-J. Boehm describes an apparatus which he has contrived for the purpose of testing the variations, under different conditions, in the absorption of gases by vegetable tissues, by starch, and by coal. One of the most interesting of his conclusions is that the cell-wall is more permeable for oxygen than for nitrogen. Dry filings of wood and of starchgrains absorb four or five times their weight of carbonic acid, while cork absorbs comparatively little. Carbonic acid, oxygen, and hydrogen all become compressed in closed cells, owing to their greater diffusibility as compared to nitrogen.

Influence of External Pressure on the Absorption of Water by Roots.-J. Vesque has carried out a series of experiments on this subject, chiefly on two plants, one woody, the oleander, and the other herbaceous, the garden bean. The following is a summary of the results arrived at:

1. The absorption of water by the roots of the oleander depends on external pressure; it seems to augment in proportion to the difference between the external pressure and that of the air contained in the woody mass of the root.

2. Osmose does not appear to be always very active; for, in diminishing the atmospheric pressure to about 60 cm. of water, absorption is arrested.

3. In the conditions of the experiments the pressure of the internal air is not very different from that of the atmosphere. It is mostly less from zero to 9 cm. of mercury; in one instance only did the internal pressure exceed that of the atmosphere by 1 cm. of mercury.

4. The effect of pressure on the oleander is sufficient for a sudden change of barometric pressure to cause a sensible disturbance in the absorption of water by the roots.

5. The garden bean was much less influenced by external pressure, as respects the absorption of water by the roots, than the oleander. There certainly is some influence, but it is ordinarily imperceptible among fluctuations resulting from changes of transpiration or from other secondary causes.

Contrivances for the Erect Habit of Plants, and Influences of Transpiration on the Absorption of Water.§-V. Meschayeff does not agree with Schwendener's view that there is a special tissue-system for the purpose of maintaining organs in an erect condition; he considers,

* Bull. Soc. Imp. Nat. Moscou, lviii. (1883) pp. 1-13. See Bot. Centralbl., xvi. (1883) p. 145.

+ Bot. Ztg., xli. (1883) pp. 521-6, 537-50, 553-9. Comptes Rendus, xcvii. (1883) pp. 718-20.

Bull. Soc. Imp. Nat. Moscou, 1883, pp. 299-322.

on the contrary, that all the different tissues may be adapted to this special purpose.

The process of the absorption of water he explains as follows:Transpiration attracts, so to speak, upwards the osmotic force, which is met by the flow of sap from all the neighbouring parts of the stem, especially in the elongated elements. The diminution of pressure which results brings into play from below the turgidity of the stem and the elasticity of the cortex; this causes increased activity in the root, which brings about an accumulation of water in the lower parts of the plant and an increased elevation of the sap. Capillarity and air-pressure play only a secondary part.

Sap.*-J. Attfield gives an account of observations made on sap exuding from a wounded silver birch tree. A branch 7 inches in diameter, had been lopped off a tree 39 ft. high, about 10 ft. from the ground, before the leaves had expanded, leaving a wound about an inch in diameter, from which sap dropped. A bottle was suspended so as to catch the sap, and from observations it was found that the flow was apparently faster in sunshine than in the shade, and by day than by night, and altogether amounted to about 5 litres a day; this had been running for 15 days, but how long it would continue is uncertain. The sap was clear and bright, sp. gr. 1.005, had a faintly sweet taste and a slightly aromatic odour. After 12 hours it deposited a trace of a sediment, which, when examined microscopically, was found to consist of parenchymatous cells and a few so-called spherecrystals. The liquid contained 99 per cent. water and 1 per cent. solid matter, which was composed mainly of sugar, 91 per cent., the other constituents being ammonium salts, albuminoids, nitrates, phosphates, and organic salts of calcium and magnesium, mucilage, and traces of nitrites and potassium salts. It had calcium and magnesium salts in solution equal to 25 degrees of total permanent hardness. It contained a ferment capable of converting starch into sugar, and when exposed to the air, it soon teemed with bacteria, the sugar being changed into alcohol.

Solid Pigments in the Cell-sap.t-The petals of flowers are far more often coloured by a pigment soluble in the cell-sap than by one in a solid granular form. Of 200 species examined by P. Fritsch, only 30 contained solid pigments in the cells either of the petals or of the fruits.

Far the most common of these solid pigments is yellow, much the greater number of yellow flowers, including nearly all yellow Compositæ, being indebted for their colour to substances of this nature. Exceptional instances of soluble yellow pigments occur in the petals of Dahlia variabilis, Althea Sieberi, and Tagetes, and in the hairs of a good many species. Solid yellow pigments are described in Impatiens longicornu, where they vary greatly in size and form, Tropaeolum majus, where the various shades of colour in the flower are due to a

* Pharm. J. Trans., xiii. (1883) pp. 819-20. Cf. Journ. Chem. Soc.-Abstr., xliv. (1883) pp. 1164-5. + Pringsheim's Jahrb. Wiss. Bot., xiv. (1883) pp. 185-231 (3 pls.).