CONCLUSION 305 



movements swini to the necks of the archegonia, through 

 a cavity, filled with sap, which is formed in the upper 

 part of the nucellus. These plants thus present a 

 beautiful transition between the Cryptogamic and Phan- 

 erogamic methods of fertilisation. The male cells are 

 conveyed for a short distance by the growth of the 

 pollen-tube, but they have to complete the journey to 

 the ovum by means of their own movements. 



A condition still more cryptogamic has just been 

 discovered by Caldwell in the Cuban Cycad Microcycas 

 calocoma, in which each pollen-tube produces no less 

 than eight pairs of generative cells, giving rise to sixteen 

 spermatozoids. This multiplication of sperm-cells, un- 

 exampled among Seed-plants, is correlated with the 

 immense number of archegonia (200 or more) produced 

 in the embryo-sac of this strange plant. 



These remarkable discoveries confirm, in the most 

 striking way, the theoretical conclusions at which 

 Hofmeister arrived forty years ago. 



From Gryrnnospernis to Angiospernis is another great 

 step, and here the gulf has not yet been bridged. In 

 Angiosperms the female prothallus has almost disap- 

 peared, and even the archegonia are no longer recognis- 

 able. The embryo-sac (the equivalent of the megaspore) 

 proceeds, after only a few preliminary divisions, to the 

 formation of the ovum, and the development of the 

 endosperm is dependent upon fertilisation, obviously 

 an expedient arrangement, for it is not formed at all 

 unless it is wanted. The processes in the pollen-grain 

 are also simplified. The great characteristic of Angio- 

 sperms is the high development of the flower and fruit. 

 Not only does the megaspore remain enclosed in the 

 sporangium or ovule, but the latter is itself enclosed in 



20 



