APPENDIX. 479 



In Selaginella the small spores correspond to the pollen- 

 grains of the Pine (and those of the Angiosperm), while the 

 large spores correspond to the nucellus cell which in the 

 Pine produces the " primary endosperm " or female prothal- 

 lus, and in the Angiosperm produces the embryo- sac. The 

 small spores of Selaginella, on being set free, germinate by 

 cutting off a small cell (representing the male prothallus) 

 from the rest of the spore, which forms an antheridium 

 similar to that of a Fern, and like it producing active swim- 

 ming male cells. The small spores (pollen-grains) of the 

 Pine, when they germinate, cut off several prothallus cells, 

 and from the rest of the grain two male cells are formed, but 

 these are not set free to swim about : they are carried to the 

 archegonium by means of the pollen -tube. 



In some Q-ymnosperms, however, a cavity filled with liquid 

 is formed in the nucellus just above the prothallus, the 

 pollen- grain bursts open, and the male cells swim in the 

 liquid of this " pollen-chamber " by means of numerous fine 

 protoplasmic threads. 



APPENDIX II. 



NOTES ON THE SOIL. 



The Soil is the medium in which land-plants may 

 place their roots in such a manner as to enable them to 

 stand erect in the light and air, and it is a storehouse of 

 moisture for the use of plants. The productiveness of a soil 

 depends largely on the amount of water it can hold, and on 



