GYMNOSPERMtE. 



Ill 



in situ on the plants ; and already in the plants last described they have a tendency 

 to become less readily detached than the microspores. This stage may have existed 

 among the extinct allies of the Selaginellas, and we shall meet with it in the 

 Gymnosperms. 



The alternation of generation which is so eminently characteristic of the Cryptogams 

 takes place within the seed of Phanerogams. The second generation, which is absent 

 altogether in Algge, and so inconspicuous in the Mosses that it never develops beyond the 

 fruit-like cup in which the spores are produced, preponderates in the Ferns, whilst in the 

 Gymnosperms the first generation is so completely hidden that it never emerges from the 

 seed. We have thus seen that, if we omit the Pungi, the progress of evolution, from the 

 simplest cellular plant to the most complex vascular plant, required that reproduction by 

 sexual functions should be accomplished during a certain stage by means of a separate 

 and special generation. The first trace of such a dual generation is to be found in the 

 capsule of the Mosses, where the second generation is rudimentary, and has no separate 

 existence. A host of intervening forms must have disappeared between this and the next 

 group, the Perns, for in these not only is the second generation thorouglily distinct, but the 

 first has sunk into a short-lived and humble cellular plant, while the second has developed 

 Into a magnificent vascular plant which sometimes attains tree-like proportions. The first 

 generation, now subordinate, is soon destined to disappear altogether, and in the Rhizocarps, 

 as already mentioned, a vast stride is made towards this consummation. Two separate 

 kinds of spores are produced, in the larger of which the once independent first generation 

 appears as an inclosed cellular mass within which the female organs are developed, so that 

 practically the larger spore has become a seed. With the next step in the progress of 

 evolution, the slender line dividing Cryptogams from Phanerogams is crossed. The Cycads 

 are the nearest on the other side of this dividing line, and in them germination takes 

 place in the macrospore or seed, while it is still attached to the plant, instead of after it 

 has been shed.^ 



Before passing on, however, to the true Gymnosperms, we have to notice a consider- 



^ Before dealing with these it is well to become familiar with the terms used by botanists in speaking 

 of the organs of Phanerogams, which are different from those used for the functionally corresponding 

 organs iu Cryptogams. 



Cryptogams. 



Gymnosperms. 



Arcliegonium, 

 Antheridia. 



Equivalent to 



Corpuscle. 

 Anther. 



Endosperm (part of the seed). 



Thallus and Prothallium. 



Sporogone. 

 Microspore. 

 Macrospore. 



» 



Plant. 



Pollen-grain. 



Embryo-sac, oosphere, the germinating cell (part of 



Microsporangium. 

 Macrosporangium. 

 Spore-bearing leaves. 



» 



SI 



»» 



the seed). 

 Pollen-sac. 

 Ovule. 



Stamens and carpels. 



