74 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Influence of the Surrounding Medium on the Growth of Roots.* — 

 As the result of experiments on Lupinw albus, J. Arker states that the 

 rapidity of the growth of the roots is increased when a current of atmo- 

 spheric air is passed through the soil in which they grow (or through the 

 water in the case of aquatic plants). In the open air, on the other hand, 

 the growth of roots is extremely slight. 



(3) Irritability. 



Reaction of Leaves to Traumatic Stimulation.! — According to 

 Dr. F. F. Blackman and Gabrielle L. 0. Matthaei, leaves of the cherry- 

 laurel or oleander will retain their vitality for weeks or even months 

 after being cut off, if kept in the dark and supplied with water ; a callus 

 being formed in the former case over the cut surface ; while in the latter 

 case a large number of adventitious roots are produced from the stump 

 of the leaf-stalk. If a clean cut be made through the substance of the 

 leaf (cherry-laurel), or even if the leaf be cut into a number of strips, no 

 healing reaction will follow, only the cells which are actually cut through 

 being killed. But if patches of cells in the leaf are killed, the sur- 

 rounding tissues will always react by cutting off and exfoliating the 

 injured patch, so that it drops out of the leaf, leaving a hole. The mode 

 of formation of the new tissue is described in detail. 



Irritability of the Higher Plants.:}: — M. J. Massart defines as the 

 " equilibrium of reaction " (equilibre reactionnel) the position ultimately 

 attained by organs, when subjected at the same time to various reflex 

 actions, each of which tends to bring about a displacement of its own. 

 There are two sets of reflex action, one having its source in the part of 

 the organ which displays curvature, the other in the apex of the organ. 

 The author has especially studied the phenomena of irritation in the 

 climbing species of Ficus, which have three kinds of aerial root differing 

 from one another in their origin and in their sensitiveness : — early ad- 

 hesive roots, later adhesive roots, and nutrient roots. 



(4) Chemical Changes (including- Respiration 

 and Fermentation). 



Formation of Proteids. § — According to W. Zaleski, none of the 

 theories at present propounded fully account for the formation of the 

 proteids in plants. He brings forward evidence to show that it may 

 take place both from organic nitrogen compounds and from nitrates, even 

 in the dark, though it is greatly promoted by light. A good material 

 for demonstrating the formation of proteids out of organic nitrogen com- 

 pounds in the dark is the bulbs of Allium Cepa. It does not take place, 

 as has generally been stated, at the cost of the asparagin, but of other 

 unknown nitrogen compounds. The regeneration, or secondary formation 

 of proteids out of the products of the decomposition of these substances 

 is illustrated in the case of etiolated seedlings of Lupinus angustifolius ; 



* Die Beeinflussung d. Wachsthuma d. Wurzeln durch d. umgebende Medium 

 Erlangen, 1900, 76 pp. See Bot. Centralbl., lxxxvii. (1901) p. 433. 



t Ann. Bot., xv. (1901) pp. 533-46 (1 pi. and 5 figs.). 



X Acad. R. Belg. Bull. CI. Sciences, 1901, pp. 547-9. 



§ The Conditions of the Formation of Proteids in Plants, Charkow, 1900 

 (Russian). See Bot. Centralbl., xxxvii. (1901) p. 277. Cf. this Journal, 1901, p. 558. 



