778 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Formation of Tubers.* — Herr H. Vochtinghas investigated the cause of 

 the formation of underground tubers, which he believes to be primarily the 

 absence of light, and secondarily an abundant supply of water. Tubers 

 are, however, frequently formed above ground, and even sometimes on parts 

 which are fully illuminated. Their production is then due to internal 

 causes perpetuated by heredity. Tubers may be either annual as in the 

 potato and artichoke, or perennial as in species of Begonia. 



Positively geotropic Shoots of Cordyline australis.t^ — Prof. F. 0. Bower 



found that when stems of this plant assumed an oblique or horizontal 

 position by reason of the weight of the head of leaves, axillary shoots were 

 formed on the lower side pointing directly downwards ; the apex of these 

 shoots remaining covered with scale-leaves. We have here a special 

 adaptation for the mechanical and physiological support of a weakly axis. 



Structure and Development of the Suckers of Melampyrum pratense.| 

 — M. Leclerc du Sablon states that the primary cause of the formation of 

 the suckers of Melampyrum pratense seems to be contact with a body con- 

 taining nutritive matter of use to the plant. A small protuberance is 

 formed proceeding from the cortex; the cells composing the two layers of 

 the cortical parenchyma elongate radially, and are then divided by septa in 

 different directions. The cells of the endoderm then elongate radially and 

 divide in the same manner, and finally the cells of the pericycle are divided 

 by tangential septa. The sucker is composed of a mass of homogeneous 

 parenchyma, the cells of which are filled with protoplasm which is more or 

 less dense. 



Ascidia of Cephalotus follicularis.§ — M. P. Maury states that the leaves 

 of Cephalotus follicularis are of two kinds ; some have an entire limb, 

 and are oval ; the others are ascidia, and have a cylindrical petiole. A 

 transverse section of the petiole made about a centimetre from the point of 

 attachment of the ascidia shows seven fibrovascular bundles disposed in 

 a circle. Near the point of attachment the circle of bundles is divided into 

 two arcs : one above, composed of three bundles ; the other lower, composed 

 of four. The cells in the epidermis of the ascidia are more or less sinuous. 

 Stomata are present ; the guard-cells on the side of the opening are pro- 

 vided with cellulose thickenings. 



The author divides the interior of the ascidia into five divisions: — 

 (1) The interior face of the oiierculum, (2) the neck, (3) the middle 

 portion, (4) the lateral coloured patches, and (5) the lower portion. 



Histology of Vine-leaves. |] — In reference to the current statement that 

 the spores of Peronospora viticola put out filaments which find their way 

 into the tissue of vine-leaves through the stomata, Sig. P. Pichi has 

 examined the leaves of several species of Vitis and Cissus, and finds uni- 

 formly an entire absence of stomata from the upper surface, while they are 

 present in large numbers on the under surface and in smaller numbers on 

 the leaf-stalk. The cells of the upper epidermis of the leaf differ from 

 those of the under epidermis chiefly in the folding of their walls. 



Structure and Development of Palm-leaves.l — Herr A. Naumann has 

 undertaken an examination of the history of development of the pinnate or 

 otherwise compound leaves in a number of species of palm : — Phoenix dacty- 



* Vochtiug, H., Ueb. d. Bildung der KnoUen, 55 pp., 5 pis., and 5 figs., Cassel, 1887. 

 See Bot. Centralbl., xxx. (1887) p. 339. 



t Kep. Brit. Assoc. BirmiDgham Meeting, 1886, p. 699. 



J Bull. Soc. Bot. France, xxxiv. (1887) pp. 154-8. § Ibid., pp. 164-8, 



II Atti Soc. Tosc. Sci. Nat., 1887, Proc. Verb., pp. 197-8. 



i Flora, Ixx. (1887) pp. 193-202, 209-18, 227-42, 250-7 (2 pis). 



