458 



BOTANY OF THE LIVING PLANT 



The climax of the sporophyte-generation is the formation of 

 spores. It is better to call those spores which follow immediately 

 on the tetrad-division specifically tetraspores. The Archegoniatae 

 probably sprang from some Algal source which had its chromosome- 

 cycle already defined, and produced spores which were all alike 

 (homosporous). The earliest land-plants were similarly homosporous. 

 In the first instance a high output of spores was the end to be gained, 



Fig. 354. 



Adult plant of Dryopteris (N ephrodium) Filix-mas, grown in the open. Much reduced. 

 An example of the Sporophyte.or diploid generation of a Fern, established independently 

 in the soil. 



and the whole development of the sporophyte in the primitive Arche- 

 goniatae serves this object, though with different degrees of efficiency. 

 In the dependent capsule of the Bryophytes life is short. Spore- 

 production happens once for all in each individual. All the spores 

 of one capsule mature at once, and the capsule itself dies. It is the 

 gametophyte of a Moss that perennates. But in the Pteridophytes 

 the gametophyte is short-lived. It is the neutral generation which is 

 predominant, rooted in the soil, and usually perennial. The plant may 

 in that case produce not one crop of spores only, but many in successive 

 years. Moreover, in the more advanced types a succession of separate 



