SPERMATOPHYTES—GYMNOSPERMS 
277 
The petiole of the leaf and the peduncle of the ovule look alike; 
but transverse sections show two bundles in the petiole and four in 
the peduncle. Both cut easily in paraffin. 
Spermatogenesis. —The entire staminate cone, even at the time of 
shedding pollen, can be cut in paraffin. For the latest stages, how¬ 
ever, it is better to remove the sporophylls and cut them separately, 
since the sections must not be thicker than 5 /*, if they are to show 
the internal structures of the pollen grain. 
The young staminate cones become recognizable in June; by 
September, they have nearly or quite reached the spore mother¬ 
cell stage, but the division of the spore mother-cell does not 
take place until the following April. In these early stages the 
bud scales should be carefully dissected away before fixing. Pollen 
is shed early in May. Fix in chromo-acetic acid, with or without 
a little osmic acid, cut 5 n thick, and stain in iron-alum haema- 
toxylin. There are four cells in the pollen grain at the time of shed¬ 
ding (Fig. 97). 
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 0.25 mm. 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 special chromo- 
acetic-osmic-acid solution is better than one with less acetic acid. 
Hot alcoholic corrosive sublimate-acetic acid will cause very little 
