ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 273 



the epidermal cells ; these cells are elongated in a radial direction, while 

 they lengthen rather in the tangential direction when grown in moist air ; 

 in the former case the outer parenchymatous cells of the cortex are usually 

 strongly coUenchymatous, only slightly in plants grown in moist air ; the 

 bast-fibre-bundles and xylem-portions are more strongly developed, the 

 vessels especially being larger, and having thicker walls. The conditions 

 of transpiration not only affect the quantity of different tissue, but cause 

 the actual formation or disappearance of tissues. Plants grown in moist 

 air have usually longer internodes and leaf-stalks, less indented leaves, and 

 less hairiness. 



The author maintains that the transpiration-current takes place in the 

 cavities, and not in the membrane of the xylem-elements. 



Chlorovaporization,* — M. P. Van Tieghem calls attention to the 

 difference between the process which he calls by this name, and transpira- 

 tion. The latter is a function of all living beings, and of all parts of plants 

 whether containing chlorophyll or not, and takes place in darkness as well 

 as in light, though it is promoted both by light and by a high tempera- 

 ture. Chlorovaporization, on the other hand, is a function belonging 

 exclusively to chlorophyll, taking place only from the chloroleucites, and 

 only under the influence of rays of light of a certain refrangibility. It is, 

 in fact, a purely physical phenomenon independent of vital energy, and is 

 much more nearly allied to the assimilation of carbon than to true tran- 

 spiration ; it is probable that, like assimilation, it would be completely 

 arrested by the action of anaesthetics, while transpiration is not suspended 

 by them. 



Influence of Cold on the Movements of the Sap.f — By the use of the 

 manometer, especially in the case of the sycamore tree, M. Leclerc du 

 Sablon has established that during periods of frost, whenever a higher 

 temperature thaws the sap, the pressure is unusually great, but varies 

 greatly in different parts of the tree. During days of thaw, the pressure 

 becomes very strong towards the middle of each day, decreasing then 

 rapidly towards evening. On days when the temperature is more uniform, 

 either warm or very cold, the pressure is also more uniform. If the stem 

 is wounded under these conditions, the sap escapes in abundance. 



The explanation usually given to the similar phenomenon of weeping, 

 viz. root-pressure, or the endosmotic force in roots, hardly appears to 

 serve in this case. 



(7) Chemical Processes (including Fermentation). 



Inversion of Sugar by Pollen-grains. | — M. P. Van Tieghem shows, 

 by renewed experiments, in the cases of the pollen of the crocus, hyacinth, 

 narcissus, wallflower, and violet, the power of converting sugar into inverted 

 sugar. This inversion exists ready formed in ripe pollen-grains. The 

 same result, though in a feebler degree, is produced by the spores of 

 Lycopodium, and of some ferns. The quantity of invertin present in 

 some pollen-grains must be very considerable, judging by the small 

 amount of pollen required to produce a considerable quantity of glucose. 



y- General. 

 Symbiotic ¥ormations.§ — Herr A. N. Lundstrom distinguishes between 

 such examples of symbiosis as are antagonistic (cecidia), and such as are 



, * Bull. Soc. Bot. France, viii. (1886) pp. 152-5. t Ibid-, PP- 208-11. 



X Ibid., pp. 216-8. 



§ SB. Naturvet. Studentsallsk. Upsala, Sept. 28, 1886. See Bot. Centralbl., xsviii, 

 (1886) p. 282. 



