112 



ELEMENTARY STUDIES IN BOTANY 



have disappeared from ordinary sight, and it is not sur- 

 prising that the large and conspicuous sporophyte is thought 

 to be the whole of the plant; it is certainly the whole of 

 the plant in sight. To find the gametophytes, one must 

 look within the microspores and megaspores with a micro- 

 scope. 



It is instructive to trace the history of the gametophyte 

 and sporophyte generations through the great groups of 

 plants. In Bryophytes, the gametophyte is the conspicu- 

 ous individual, the sporophyte being dependent upon it and 

 being not much more than a spore-case. In the Pterido- 

 phytes, the sporophyte has become the conspicuous individual, 



but in most Pterido- 



Bryophytes Pteridophytes Spermatophytes 



FIG. 92. Diagram illustrating the advance of the 

 sporophyte and the decline of the gametophyte 

 through Bryophytes, Pteridophytes, and Sperma- 

 tophytes. 



phytes the 

 phyte is a free and 

 independent individ- 

 ual, although rela- 

 tively very small. In 

 the heterosporous 

 Pteridophytes and in 

 all the Seed-plants, 

 the gametophytes are 



neither free nor independent, and have disappeared from 

 view within the spores that produce them. The accom- 

 panying diagram (Fig. 92) will illustrate the gradual 

 advance of the sporophyte and the gradual decline of the 

 gametophyte through the plant kingdom. 



64. Summary. The most, important fact in connection 

 with the Pteridophytes is the appearance of an independent 

 sporophyte, which is now the conspicuous generation. With 

 the appearance of an independent sporophyte there are asso- 

 ciated three structures not found in the lower groups of plants : 

 the vascular system, the sporophyte leaves, and the root. 



A second important fact is that among the Pteridophytes 

 the strobilus appears, which is the precursor of the flower. 



