670 SUMMARY OF CURKENT RESEARCHES RELATING TO 



water with those grown in ordinary soil, M. H, Jumelle comes to the 

 conclusion that the presence of mineral substances favours the produc- 

 tion of jDarenchyme rather than that of supporting tissue. During the 

 earliest stages of development no difference conld be detected in the 

 development of the sets of plants grown under different conditions ; but 

 after about 60 days, when the number of leaves exceeds five or six, in 

 the former set the leaves were found to be small and bright green, the 

 internodes long and slender ; in the latter the leaves were large and 

 yellowish-green, the internodes short and thick. The difference appears 

 to be due less to the absence of the salts themselves than to the accom- 

 j)anying diminution of the water of constitution. 



Trophilegic Function of Leaves.* — Prof. G. Arcangeli calls atten- 

 tion to the observations of Goebel f on the heterophylly of the leaves of 

 tropical species of Plafycerium and other ferns. He points out that the 

 presence of leaves of a shell-like fo^-m is not peculiar to ferns, but occurs 

 also in many flowering plants ; the function of these leaves being, if not 

 the direct absorption of water, the collection of food-material for the use 

 of the plant. He proposes for this function, to which he thinks too 

 little attention has been paid, the term trophilegic. 



Movement of Sap in the Wood.f — According to Prof. R. Hartig, 

 the movement of fluid in woody stems takes place chiefly in the outer 

 layers of alburnum, the inner layers of alburnum forming a reservoir 

 where it is stored up when not in motion. In Coniferse the tracheides 

 together with the medullary rays are certainly the organs of conduction 

 from one layer to another ; while in Dicotyledons it is probably the 

 vessels in which this movement of the sap takes place. The vessels, 

 which diminiish the weight of the wood by their size and by the thinness 

 of their walls, run downwards from the leaves through the corresponding 

 annual ring to the root. In a beech 143 years old the number of vessels 

 in the youngest annual ring was estimated at 116,000. 



Dr. Hartig farther replies § to Wieler's criticisms || on his previotisly 

 published results, repeating his reasons for coming to the conclusion 

 above stateil as to the ordinary course of the movement of fluids. 



Exchange of Gases in Submerged Plants.^ — M. H. Devaux has 

 studied, by means of a mechanical apparatus, the mechanism of the 

 exchange in gases in plants entirely submerged, the experiments having 

 been made chiefly on Elodea canadensis. 



The escape of gases may take place either by diffusion through the 

 cell-walls or in the form of bubbles; the former mode being very 

 analogous to that which would take place across an immobile liquid 

 plate. The entrance by diffusion takes place in the same way, whether 

 the plant grows in air or in water. Bubbles disengaged from the 

 interior of the plant are always the result of injury; and from an 

 examination of these it was found that the internal atmosphere of sub- 

 merged plants has very nearly the same composition as the external air, 



* Nuov. Giorn. Bot. Ital , xxi. (1889) pp. 272-6. 

 t Of. this Journal, 1888, p. 90. 



X SB. Bot. Vercin Miinchen, Feb. 11, 1889. See Eot. Centmlbl., xxxvii. (1889) 

 p. 418. 



§ Ber. Deutscli. Bot. GeselL, vii. (1889) pp. 89-94. 

 II Cf. this Journiil, ante, p. 2.il. 

 ^1 Aun. Sci. Nat. (B<it), ix. (1889) pp. 35-180. 



