Spermatophytes Gymnosperms 



257 



For a study of the ovule and the structures within it, better 

 preparations will be obtained by carefully cutting off the pair of 

 ovules from the scale: Fix in chromo-acetic acid with a little osmic 

 acid. In free nuclear stages of the female gametophyte, which begin 

 in the autumn, are interrupted by winter, and are completed in May, 

 plasmolysis is likely to occur. After walls appear there is less danger. 

 From the middle of May to the first of July collections should be 



A B 



c 



FIG. 89. Pinus Laricio: A, top of prothallium with an archegonium just before 

 the cutting off of the ventral canal cell; fixed in Flemming's weaker solution and stained 

 in Haidenhain's iron-alum haematoxylin ; collected June 18, 1897; B, C, and D, early 

 stages in the development of the embryo; fixed in chromo-acetic acid and stained in 

 safranin, gentian-violet, orange; collected July 2, 1897. X104. 



made at intervals of two or three days, since during these six weeks 

 the gametophyte completes the free nuclear stage and develops 

 cell walls, the archegonium completes its entire development, the 

 egg is fertilized, and the sporophyte may reach the suspensor stage. 

 For preparations like that represented in Fig. 89, A, it is a good plan 

 to remove the endosperm with its archegonia from the ovule. Fixing, 

 infiltration, and cutting will then occasion but little trouble, and the 

 whole ribbon may be got upon a single slide. However, at this stage 

 the pollen tubes with their contents are rapidly working their way 



