458 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Tho author concludes that it is the protoplasm which is the active 

 agent in the movement of tho leaves, and not the cell-wall or the cell-sap. 

 It is not conceivable that the physical properties of the cell- wall, or tho 

 osmotic properties of tho cell-sap, should bo affected in such opposite 

 ways by these alkaloids. 



In the course of theso observations Dr. Vines noted some points in 

 the physiology of tho movements of the leaves of Mimosa which seem 

 to have been hitherto overlooked : the fall of the petiole is in no caso 

 caused by artificial darkness during the daytime, but takes place only in 

 tho evening, when the general tension diminishes ; the secondary petioles 

 are likewise unaffected by darkness during the daytime, and they are 

 sensitive to mechanical stimulation only when the leaf is young. 



Geotropism.* — Herr W. Saposhnikoff defends the older theory of 

 Knight and Hofmeistcr, of the passive geotropic curvature of roots, 

 against the new theory of active curvature. Roots from which the apex or 

 heaviest part has been removed, are geotropic in the air, but show no 

 curvature in water. Microscopic examination of the curved portions of 

 roots show that the lower part of the cork-parenchyma of the root is 

 thicker than the upper part. In the root, as in the stem, the lower part 

 has a tendency to grow more rapidly than the upper part. 



y. General. 



Ceeidium of Nematus Caprese.f — Herr M. W. Beyerinck states that 

 the galls produced on various species of willow by the Tenthredinese may 

 be divided into two groups, one having a globular form and being con- 

 nected with the leaf by a short stalk, tho other forming a thickening on 

 both the upper and under side of the leaf. To the former group belong 

 the ceeidium of Nematus viminalis on Salix purpurea, and that of 

 N. pedunculi on S. aurita ; to the latter that of N. Caprese, which is 

 most common on S. amygdalina, alba, and fragilis, less frequent on 

 S. babylonica and pentandra. 



Nematus Caprese occurs in two generations. At the end of May the 

 small saw-wasp pierces with its saw the young leaves in the terminal 

 bud of S. amygdalina, making a triangular puncture in which the egg is 

 laid, and the orifice is closed by a drop of mucilage from the poison- 

 bladder. Hypertrophy sets up immediately in all the tissues of the leaf, 

 and the gall attains its full development in from two to three weeks. 

 By the end of June the larva pierces the gall, falls to the ground, and 

 spins a dark brown cocoon, changing into a nymph-pupa, from which, 

 in August, the second generation proceeds fully developed. This also 

 seeks the shoots of the willow in which to lay its eggs ; the animal goes 

 through the same changes, but the cocoon is spun within the gall, which 

 falls to the ground. In the first generation the males are entirely 

 wanting, and are very rare in the second. Parthenogenesis appears to 

 take place from generation to generation without any unfavourable results. 



The formation of the gall appears to be caused neither by the egg, 

 nor by the larva, but by the action of the drop of poison injected by the 

 insect herself. The substance which produces the gall is not an ordinary 

 albuminoid, but as is probably the case also with all galls, it has all the 

 properties of a ferment. 



* Schrift. Moskauer Univ., 1887, 21 pp. and 1 pi. (Russian). See Bot. Central bl., 

 xxxiii. (1888) p. 101. t Bot. Ztg., xlvi. (1888) pp. 1-11, 17-28 (1 pi. and 1 fig.). 



