482 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tapetum, the condition in the microspore is doubtful. In the Conifer* 

 the tapetum of the macrospore is reduced, but does not form a peri- 

 plasmodium, and in the microspore it is doubtful. In the Angiosperms 

 the tapetum, even when present, forms no periplasinodium in the macro- 

 spore, but there is usually a typical one in the microspore. The author 

 then proceeds to trace the relations between the tapetum or periplas- 

 inodium and the spore-membranes, and shows how the membrane con- 

 sisted at first of a typical exospore and epispore in the Bacteria, Fungi, 

 and Algae, gradually becoming modified, until in the Coniferge and 

 Angiosperms only the exospore remains. Finally he shows how the 

 membrane of the embryo-sac corresponds with the similar structure of 

 the male organ, but has gradually been modified to suit new conditions 

 of germination, and the partially cutinized membrane of the embryo-sac 

 of Gymnosperms finally disappears in the higher Angiosperms. 



Physiology. 

 Nutrition and Growth. 



Mineral Nutrition of Vascular Plants.* — J. de Bufz de Lavison 

 publishes a paper describing a new theory as to the absorption of salts by 

 vascular plants. Experiments were made with sections of stems, wounded 

 roots, and with entire uninjured plants, and it is shown that absorption 

 of salts in the first two cases gives no indication as to the amount 

 absorbed by the entire, uninjured plant. This is conclusively proved by 

 the action of such a salt as citrate of iron, which is freely diffused in 

 the first two cases, but completely arrested by the endodermis in the 

 last case. Further, while there is no fixed ratio between the amount 

 of an iron salt in contact with the root and the small amount which 

 diffuses into the aerial portion of the plant, there is a distinct ratio in 

 the case of nitrites and chlorides of the alkaline metals and alkaline 

 earths, probably due to some complex phenomenon of assimilation. The 

 most important experiments are those of this class which prove that the 

 root exercises a qualitative selection over the salts absorbed. There 

 seems to be no anatomic cause for this, and the author believes that 

 there is some inherent character in the protoplasm of the endodermis 

 which brings about this result ; the ordinary protoplasm does not appear 

 to possess this property. Two main general conclusions may be formed, 

 viz. : 1. Salts incapable of penetrating protoplasm are arrested by the 

 endodermis and undergo a species of assimilation before passing further 

 into the plant. 2. Salts capable of penetrating the protoplasm undergo 

 a sort of filtration in the endodermis depending upon (a) the nature of 

 the plant ; (b) the nature of the salt ; (c) the condition of the endo- 

 dermis at the time of the experiment. 



Living Cells in Relation to Transpiration and Sap-flow. |— J. B. 

 Overton publishes the second paper dealing with his work on Cyperus, 

 the following being the chief results obtained. A stem 15-GO cm. high 

 will conduct sufficient water to preserve the turgidity of the leaves for 

 3 to 18 days, when a section of 5-30 cm. has been killed by steam. The 



* R6v. G6n. Bot., xxiii. (1911) pp. 177-211 (2 figs.), 

 t Bot. Gaz., li. (1911) pp. 102-20 (2 figs.). 



