CONIFERAE : THE SCOTS PINE 



315 



means of a pollen-tube and non-motile gamete, are the same in the Coniferae 

 as in Angiosperms. But in certain very primitive Gymnosperms, viz. in the 

 Cycads and Ginkgo, the gametes are themselves motile (Fig. 257), and of extra- 

 ordinary size. They are liberated from the 



pollen-tube, and have free movement before a % 



fertilisation, by means of numerous cilia, in 

 fluid present in a chamber just above the 

 archegonia. Thus they make their own way to 

 the archegonial neck. This is a specially 

 significant fact for comparison with the 

 Pteridophyta, where the male gametes are 

 always motile. 



The general effect of comparisons be- 

 tween Gymnosperms and Angiosperms is 

 to show that in the former the balance 

 between the two generations is less un- 

 even than in the latter. The complexity 

 of the sporophyte is less in Gymnosperms, 

 though its mere size may be very great. 

 The complexity of the gametophyte, both 

 male and female, is greater. But still the cycle of events in the 

 alternating generations is essentially the same as in the higher Seed- 

 bearing Plants. Such differences, slight though they may at first 

 appear, gain in importance when seen in the light given by the study 

 of the Pteridophyta. 



FIG. 257- 



End of pollen-tube of Zamia, a 

 Cycad, showing the prothallial cell 

 (), the sterile sister-cell (s), and 

 the two spermatozoids. a, before 

 movement of the spermatozoids has 

 commenced, b, after beginning of 

 ciliary motion. ( x about 75.) (After 

 Webber, from Strasburger.) 



