46 CAL/FORAYA ACADEMY OF SC/EXCES. [Proc. 30 Ser. 



and to judge from the appearance of sections studied (figs. 

 100 and loi), the upper and not the lower of the cells gives 

 rise to the embryo-sac. The outer integument appears 

 about the same time that the first divisions take place in the 

 inner archesporial cell and grows with the developing ovule, 

 but as in Naias, remains usually shorter than the inner 

 integument, which forms the micropyle. The appearance 

 of these in the mature ovule (fig. 105) shows nothing 

 peculiar. 



As the ovule develops, the growth continues stronger upon 

 its upper side, so that it is forced over more and more, until 

 it hangs almost vertically, having passed through an arc of 

 nearly 180 degrees from the position it at first occupied. 



The tube formed by the confluence of the outer margin 

 of the shoot and the carpellary leaf grows rapidly and forms 

 the cylindrical style, and its upper margins become widely 

 expanded to form the large peltate stigma. There are no 

 secretory papillae formed within the ovary for the purpose 

 of directing the pollen-tube, but the position of the ovule is 

 such that the pollen-tube must grow along the integument 

 as far as the opening of the micropyle. Whether some 

 substance is then excreted by the ovule, which directs the 

 tube into the micropyle, it would be difficult to prove; but 

 it is quite probable. 



The small size of the pollen-spores precludes the pos- 

 sibility of their depending upon the contained starch for the 

 growth of the pollen-tube until it reaches the ovary. It is 

 not surprising, therefore, to find several layers of cells sur- 

 rounding the canal of the style, with abundant protoplasm 

 and large nuclei, evidently secretory cells, presumably 

 concerned with the nourishment of the pollen-tube in its 

 passage through the style. 



The embryo-sac, as usual, arises from one of the arche- 

 sporial cells which destroys the others, and soon fills the space 

 formerly occupied by them. Owing to repeated divisions 

 in the tapetal cells, the young embryo-sac lies much deeper 

 within the nucellus than was the case with Naias (fig. 102). 

 The subsequent development in normal cases is of the usual 



