Spermatophytes Gymnosperms 251 



Pollen tubes and their structures must be studied in sections of 

 the nucellus. Fertilization, in the Chicago region, occurs about the 

 middle of September. 



Oogenesis. -Young ovules about 0.25mm. in length are found 

 about the middle of April; the megaspore mother cell and its divi- 

 sion into four megaspores are found about the first of May; the 

 free nuclear stage in the development of the female gametophyte 

 extends from the first week in May to the first week in July; during 

 July, walls appear; then the archegonium initials and the growth of 

 the archegonium, the ventral canal cell being cut off the second week 

 in September; fertilization, free nuclear division in the sporophyte, 

 and the beginning of walls may all be found before the end of Sep- 

 tember; cotyledon stages belong to October, and when the seeds 

 fall in November the embryo extends throughout nearly the entire 

 length of the endosperm. This is the winter resting stage, but, 

 planted in the greenhouse, the seeds germinate without any resting 

 period, as in the case of cycads. 



For all stages in oogenesis and development of the embryo, use 

 chromo-acetic acid. The free nuclear stages in both gametophyte 

 and sporophyte are almost sure to plasmolyze. The addition of a 

 little osmic acid may minimize the danger. Chromo-acetic acid, 

 with the chromic rather weak and the acetic rather strong, may fix 

 without plasmolyzing, and thus give better views of the general 

 structure; but material fixed in any reagent containing a large per- 

 centage of acetic acid is not likely to be satisfactory for a study of 

 chromatin. 



For sections of the entire ovule, use safranin, gentian-violet, 

 orange ; for free nuclear stages in both gametophyte and sporophyte, 

 use iron-haematoxylin with a touch of orange; for the megaspore 

 membrane, safranin seems to be the best stain. 



GYMNOSPERMS CONIFERALES 



Since Pinus is an available laboratory type, we shall describe 

 methods for demonstrating various phases in the life history of this 

 genus, hoping that the directions will enable the student to experi- 

 ment intelligently with similar forms. The dates are for Pinus 



