156 GENERAL BIOLOGY 



sections, and also the developing embryo, and diagram. 

 Germinate the seeds and trace the disappearance of 

 the endosperm. 



The record of this study may consist in notes on and 

 diagrams of the principal things observed. 



The gametophyte phase of the higher seed plant is well 

 nigh suppressed :* why, we cannot say. And sex charac- 

 ters, w^hich primarily must belong to the sexual phase, 

 are gradually extended to the sporophyte: first to the 

 spores alone, then to the sporangia and flower scales and 

 finally, in unisexual (dioecious) species, to the whole 

 organism. 



The great advance made by the spermatophytes over the 

 lower groups is in their manner of reproduction. Bryo- 

 phytes and Pteridophytes, though terrestrial, have retained 

 an aquatic mode of fertilization. Their free swimming sperms 

 are subject to vicissitudes of drouth which the seed plants 

 have largely obviated. The weak point in the life history 

 of the fern is in the development of delicate unprotected 

 prothallia from microscopic spores. The seed plant sets its 

 offspring adrift only when grown to considerable size and 

 supplied with a store of food material for further growth. 

 What chance of a living have fern spores in competition 

 with seeds ? A main reason for the dominance of the seed 

 plants upon the earth in our own time therefore lies in the 

 better start in life they furnish to their offspring. 



II. THE ANIMAL SERIES. 



We will choose among the higher animals a series of forms 

 ending with the vertebrates, and will illustrate it with three 

 types: — hydra, the earthworm and salamander, with some 

 supplemental illustrations drawn from the vertebrate group. 



*The accompaning diagram (fig. 99) is offered as an aid to the 

 beginning student who may still find difficulty in identifying its 

 remains. 



