Reproductive Structures of Vascular Plants 175 



15.4 /;) ; the origin and development of the ovule and integuments 

 (Fig. 11.3); the origin and enlargement ol the megasporocyte (Fig. 

 11.3); meiosis, (Fig. 11.4) and the four megaspores in the unparti- 

 tioned embryo sac (Fig. 15.5) . It is of interest that the embryo sac 

 of Liliiim pardalinum is narrow and the megaspores are in linear 

 order, whereas L. iimbellatum has a broad embryo sac and a cruciate 

 quartet (Fig. 15.5) . The so-called normal type, which might better 

 be named the common type, involves the formation of a cjuartet of 

 megaspores, three of which degenerate, the fourth giving rise to the 

 female gametophyte. This type occurs in maize, the legumes, tomato, 

 and many other economic plants. The preparation of each of these 

 is virtually a research task, and the reader who wishes to work on 

 any of these plants should survey the literature on the desired plant. 

 Lilium is a good subject for making preparations showing fertili- 

 zation (Fig. 15.6). Begin collecting 48 hr. after pollination and 

 make collections e\ery 12 hr. Use the killing fluids and methods 

 recommended for the embryo sac. A series of collections will show 

 stages from unfertilized mature embryo sac to young embryos (Fig. 

 15.6 fl). 



^JV^4i3 



^^^ SI. 



Fig. 15.5-rt, First binucleate stage in embryo sac of Lilium tigrinum. Note the lag- 

 ging cliromosomes; b, linear megaspores of L. pardalinum; c, cruciate arrangement 



of megaspores of L. umbcllatum. 



