ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 661 



however, the chlorophyll disappears, starch is deposited, and the layer 

 becomes a reservoir of reserve food-stuff. The cells may also hecome 

 rich in deposits of tannin and calcium oxalate, i.e. are excretory, and 

 finally, by the sclerosis of the cell-walls, the layer plays an important 

 mechanical function. 



The duration of the zone is very variable. It may perish a few 

 weeks after its formation or may remain for many years at the surface 

 of great trunks. There seems little or no relation between the nature 

 of the zone and its duration. The author also discusses the influence 

 of the pericycle on the development of the cortex and the central 

 cylinder. Thus a sclerotic pericycle may offer considerable resistance 

 to the development of bast and be an important obstacle to the forma- 

 tion of vessels. As regards its taxonomic value, the pericycle of the 

 young stem is a character of the first importance, but owing to the 

 modifications to which it is liable in later stages, varying with age and 

 even in one and the same tree, it becomes very difficult to draw con- 

 clusions of taxonomic value. As an autonomous zone, from an ana- 

 tomical point of view, the pericycle does not exist in woody axes even 

 relatively young, nor in many herbaceous stems. It is merely a con- 

 ception. The study of the evolution of the axis shows this region to 

 be a mixture of elements of the most diverse origin. As a definite tissue 

 also the pericycle has no existence. It is a pseudo-tissue subject to 

 continual additions, destructions, and modifications. Owing to the con- 

 tinual intrusion of new elements the pericycle has no definite limits or 

 contour, and cannot be regarded as " exactly delimiting the position 

 and constitution of the bast." 



Reproductive, 



Polyembryony in Gingko.* — M. T. Cook records a single case of 

 polyernbryony from Washington D.C. Two embryos were present, 

 each as complete in every respect as the single embryos except in size ; 

 their length was about three-fourths the average length of single 

 embryos. 



Histology of the Endosperm.| — W. Gardiner and A. W. Hill have 

 investigated the histology of the endosperm during germination of the 

 seed in Tamus communis and Galium tiicorne. A description with figures 

 of the macroscopic characters of the germination in Tamus is given, 

 illustrating the early production of an epicotyledonary tuber in which 

 the reserve materials of the seed are in part re-stored as starch. The 

 thick endosperm walls are, judging from their reactions to stains, pro- 

 bably composed of a reserve cellulose like that described by Gruss from 

 seeds of the date palm and other plants. Connecting threads occur in 

 groups throughout the walls which are uupitted. The progress of the 

 ferment action is centrifugal with reference to the embryo ; the fermeut 

 which proceeds from the cotyledon along a few of the threads, affects 

 first those walls of the endosperm cells which are in immediate contact 

 with it, and as the cotyledon enlarges pari passu with the disorganisa- 

 tion of the endosperm, extends its sphere of action into deeper layers. 



* Bot. Gaz., xxxiv. (1902) pp. 64-5 (1 fig.). 



t Proc. Cambr. Philosoph. Soc, xi. (190:0 pp. 445-54 (1 pi.). 



