4 I2 



THE AMERICAN NATURALIST. [Vol. XXXVII. 



spore formation and germination of the asexual spore has been 

 made the subject of careful study. It is evident that the criti- 

 cal periods of the plant's life, when the changes are the greatest, 

 come with the passing of one generation over to the next or in 

 other words at the periods of gametogenesis and sporogenesis 

 with tlie early developments following each of these processes. 

 We have now an accumulation of studies upon this subject from 

 all three of the great groups of higher plants (bryophytes, 

 pteridophytes, and spermatophytes) and in certain regions the 

 investigations have been numerous. They have uniformly 

 yielded the same results in certain particulars that have estab- 

 lished a foundation for some very interesting speculations on the 

 essential differences between the sporophyte and gametophyte. 



It will be apparent that these differences must be very fun- 

 damental because they are the basis of extensive evolutionary 

 processes with the universal tendency to separate the gameto- 

 phyte and sporophyte further and further from one another in 

 structure and life activities. From the conditions among the 

 bryophytes in which the sporophyte is so closely associated with 

 the gametophyte as to have been called its fruit by the early 

 botanists, we pass through the pteridophytes to the spermato- 

 phytes where somewhat analogous conditions are found in which, 

 however, the relations between the two generations are exactly 

 reversed. Among the seed bearing plants the gametophyte has 

 become so reduced as to live parasitically upon the sporophyte 

 passing its life in the interior of the asexual generation which is 

 thus made the phase that performs the vegetative activities that 



of plant morphology than that which traces the evolution of the 

 sporophyte and degeneration of the gametophyte as one passes 

 from the liverworts to the higher plants. There are involved in 



