CLUB MOSSES 



429 



This formula also indicates the life history of any seed 

 plant, except that in seed plants 

 there may be two kinds of strobili. 



Surely Selaginella throws light 

 upon the evolution of seed plants ! 

 We are not yet done, however. 

 There is yet another feature of 

 Selaginella to be considered which 

 is also a feature of seed plants. 

 This other feature is that the game- 

 tophytes do not escape from the 

 spores which produce them. No 



Fig. 221. — Sections through 

 spores of Selaginella as seen 

 through a microscope. This 

 shows their actual difference 

 in size. 



Fig. 222. — Selaginella. Sketches show- 

 ing stages in the germination of the 

 microspore and the development from 

 it of the male gametophyte. A, ma- 

 ture microspore. B, the microspore 

 containing two cells; it has new 

 ceased to be a spore; the male 

 gametophyte has begun. C and D, 

 later stages in the development of 

 the male gametophyte; D shows the 

 sperms ready to be discharged and 

 shows that the male gametophyte, 

 even when mature, does not escape 

 from the old microspore wall. 



longer do we find the spores 

 producing little green inde- 

 pendent gametophytes such 

 as we noted in the true ferns. 

 Instead of that, the gameto- 

 phytes remain largely within 

 the walls of their parent 

 spores. Remember that a 

 spore is but a single cell. 

 When it becomes two cells, it 

 ceases to be a spore ; it be- 

 gins to be a gametophyte. 

 So a structure of even a few 

 cells held within the walls of 

 its parent spore is as truly 

 a gametophyte as a much 

 larger green structure, such 

 as a moss plant, which soon 

 leaves its spore behind it. 

 This matter of the size of 



