82 MORPHOLOGY OF SPERMATOPHYTES 



and Sequoia), after considerable increase in size, presumably 

 pass through the reduction division, although this has never been 

 definitely observed. The reduction number of chromosomes 

 was observed by Dixon ^^ in the endosperm cells of Pinus sil- 

 vestris ; while Blackman *'' and Chamberlain ^^ definitely 

 counted twelve chromosomes in the endosperm of Pinus silves- 

 tris and Pinus Laricio respectively. In the case of Larix Stras- 

 burger ^* has demonstrated the existence of a row of three cells 

 derived from the mother cell (Eig. 61), and in Taxus the same 

 number and sometimes more, in both cases the lowest cell becom- 

 ing the fertile megaspore. The same investigator makes the 

 general statement that Thuja, Pinus silvestris, and Pinus Pu- 

 milio are essentially similar. We have recently discovered this 

 stage in Pinus Laricio (Fig. 106), too late to include the figure at 

 this place. A row of four potential megaspores is very evident, 

 the lowest one becoming functional, the other three appearing 

 for a time as a densely staining cap. In the preparation figured 

 the original wall of the mother cell is sharply defined, but the 

 walls between the disintegrating cells are very indistinct. 



In case several mother cells are functional, as in Taxus and 

 Sequoia, several megaspores may begin to enlarge simultane- 

 ously, but one soon dominates, and enlarging at the expense not 

 only of the other megaspores, but also of the adjacent sterile 

 tissue, becomes the single very large fertile megaspore of the 

 sporangium. Sometimes the sterile megaspores are somewhat 

 prominent in the nucellus, and in Sequoia Shaw ^* records them 

 as clustered about the upper third or fourth of the remarkably 

 elongated functional megaspore. 



The usual account of the germination of the megaspore and 

 the development of the archegonia has been derived from the 

 publications of Hofmeister ®' ^^ and Strasburger,^''' ^'^' -^' -■'' ^^ 

 but recently much has been added in the way of detail. Very 

 early in its history, long before it has attained its fertilization 

 size, the megaspore begins to germinate, and embryo sac * and 

 gametophyte continue growth together until the nucellus is 

 largely replaced. The sequence of events is much the same as 



* For convenience we make an arbitrary distinction between megaspore 

 and embryo sac, the former being the true uninucleate spore, the latter the 

 persistent and growing wall of the megaspore, which continues to invest the 

 gametophyte. 



