436 SUMMARY OF CDRUENT RESEARCHES RELATING TO 



important of them must bo osmose and the filtration necessarily connected 

 with it. 



Prof. Schwendener specifies those natural orders in which there are no 

 other mechanical elements than more or less thick-walled libriform cells 

 with bordered pits ; those which possess, in addition to these stereids, 

 libriform cells with a few unbordered pits ; those which have a homo- 

 geneous libriform or stereome with a few unbordered pits ; and finally, 

 those in which the different genera differ from one another on these points. 



Periodicity in the Phenomena of Bleeding-.* — Herr C. Kraus has 

 detected a daily periodicity in the chemical nature of the sap exuded from 

 cut stems (turnip, maize, sunflower, hop), indicating corresijonding varia- 

 tions in the root-pressure. The most common sequence exhibited was : — 

 slightly alkaline in the morning, strongly acid in midday, and nearly 

 neutral in the evening. Before the close of the " bleeding " the sap 

 ceased to exhibit any acid reaction throughout the day. 



Absorption of Water by Terrestrial Organs.f — Herr L. Kny gives 

 more in detail the experiments according to which Dipsacus laciniatus and 

 Fullonum, alone among the plants examined, possess the power of absorb- 

 ing water in the form of drops through their leaves, the latter species 

 having it to the greater degree. Even here, however, the amount 

 absorbed from the trough formed by the connate bases of the opposite 

 leaves is very small comj)ared to that suj)plied through the root. No 

 very striking difference was found in the anatomical structure of the 

 tissue of which this trough is composed, as comjiared with that of other 

 parts of the plant. The author does not consider that the glandular 

 hairs observed by Prof. F. Darwin on this part of the leaf take any part 

 in the absorption of the water. 



Structure and Coiling of Tendrils. J — M. Leclerc du Sablon has inves- 

 tigated the anatomical causes of the coiling of tendrils in the CuciirbitaceaB, 

 Passifloracea), Smilaceae, and Ampelidea3, and in other genera in which 

 they occur. He finds a constant relation between the sensitiveness of any 

 region of the tendril and its anatomical structure. The sensitiveness of a 

 surface is proportionate to the number of thin-walled fibres or of very 

 elongated cells in its vicinity. Their anatomical structure is, however, 

 only one factor in bringing about the coiling of tendrils ; their form, 

 flexibility, and movements being other factors. The author does not 

 consider the unequal growth of the two sides of the tendril as an adequate 

 explanation of the cause of its movements. The helicoid contraction of 

 the free part of a fixed tendril he regards as quite independent of the 

 extension of the coiling round a support ; it should rather be compared 

 to the spontaneous coiling of a tendril which has not reached any suj)port. 



Theory of Twining. — Herr H. Ambronn replies § to the criticisms of 

 Wurtmaun || on his own and Schwendener 's theories on the causes of 

 the twining of climbing stems. He charges Wortmann with confusing 

 the elementary ideas of dextrodromal and sinistrodromal torsions, and 

 especially contests his aphorism that " the movement of coiling is identi- 

 cal with circumnutation." 



* Ber. Deutsch. Bot. Gesoll., iv. (1S86) pp. 319-22. 



t Ibid., Gen.-Versamral., pp. xxxvi.-lxxiv. Cf. this Journal, ante, p. 119. 

 X Bull. Soc. Bot. France, viii. (18SG) pp. 480-3, and Ann. Sci. Nat. (Bot.), v. (1887) 

 pp. 5-50 (3 pis.). 



§ Ber. Deutsch. Bot. Gesell., iv. (1886) pp. 3G9-75. 

 Jl See this Journal, ante, p. 118. 



