ZOOLOGY AND BOTAXY, MICROSCOPY, ETC. 441 



members of the Nymphfeacete, and finds that the development of the 

 embryo-sac is the same in all species. The endosperm nucleus divides, 

 and the antipodal daughter-nucleus enters a tube which penetrates the 

 nucellus, and which is used for transferring food from the nucellus to 

 the endosperm. The endosperm in NijmpJum and Castalia is cellular, 

 while in Brasenia purpurea and Cabomba piauhiensis it is nuclear at first, 

 but cellular later. In NymphcBa advena the spherical mass of embryonic 

 cells gives rise to a cotyledonary ridge and suspensor ; in other species 

 the embryos consist of a single row of cells, which give rise to a 

 spherical embryo with a suspensor. Later on a crescent-shaped cotyle- 

 donary ridge is developed around the embryo, and two cotyledonary 

 lobes are formed which may easily be mistaken for cotyledons. 



Development and Embryology of Melilotus alba.* — W.J. Young has 



studied the development of Melilotus, and finds that, while the floral prgans 

 appear in the order, sepals, stamens, carpel, petals, the last three may 

 appear simultaneously. The archesporium is of late differentiation, and 

 the tapetum is limited. The megaspore mother-cell gives rise directly 

 to the embryo-sac, which increases in size before fertilisation, replacing 

 all the tissue within the integuments. The polar nuclei do not fuse until 

 just before fertilisation. The ovule is first anatropous, later campylo- 

 tropous. When there are several endosperm-nuclei in the embryo-sac, 

 the egg divides to form a :3-celled pro-embryo, the terminal cell of 

 which gives rise to the embryo, and the second cell to the suspensor. 

 The early development is Hke that of Gapsella, but the dermatogen 

 appears later. The embryo-sac is nourished by means of a nutritive 

 jacket formed by the inner integument. The endosperm in the chalazal 

 region acts as a haustorium in the later stages. After formation of the 

 seed-coat, nutritive material passes through the outer columnar cells to 

 special inner tracheids, which then distribute it to the surrounding 

 tissue. 



Physiology- 

 Nutrition and Growth. 



Transpiration Current in Plants.f — ^H. H. Dixon has made inves- 

 tigations upon the transpiration current, with special reference to the 

 results obtained by Ewart, whereby the latter was led to believe that a 

 head of six to thirty-three times the height of the plant would be 

 required to move water in the stems of plants at the velocity of 

 transpiration current. The author shows that there were three reasons 

 for regarding the above conclusion as incorrect, viz. : (1) The velocity 

 of flow given by Ewart was probably much in excess of the maximum 

 velocity of the current in the uninjured plant ; (2) the velocity in high 

 trees is not uniform, but falls off from below upwards ; (3) the estimate 

 of the resistance was excessive. The present experiments show that the 

 transpiration of the isolated branches used by Ewart is not the same as 

 for all the branches under normal conditions. Also, the water supply 



* Proc. Indiana Acad. Sci., 1905 (1906) pp. 133-41 (3 pis.). 

 t Proc. Roy. Soc, Series B, Ixxix. (1907) pp. 41-57 (5 figs). 



Aug. 21st, 1907 2 G 



