I54 GENERAL BIOLOGY 



certain : the antipodal nuclei disintegrate and the endo- 

 sperm nuclei fuse (and sometimes the second sperm nu- 

 cleus fuses with them) , before undergoing further division 

 to form the endosperm. 



Subsequent development is wholly comparable with that 

 of the pine already discussed, save that in many of the 

 higher spermatophytes the endosperm is wholly absorbed, 

 and the matured seeds contain only the embryo, and are 

 without endosperm. 



Study 21. Spermatophyte structure. 



Materials needed: Stems and leaves of chickweed or 

 other herbaceous plant. Miscellaneous wood specimens, 

 green and finished. Sections and slide mounts showing 

 vascular bundle elements. Stems and leaves of monocoty- 

 ledons. 



No specific program need be given for a single study of a 

 subject that offers so vast an array of possible materials. 

 Suffice it to suggest that the student use whatever materials 

 are at hand as a means of identifying in the higher plants 

 the tissues already seen in the pteridophytes, and to dis- 

 cover the new features of tissue arrangement presented by 

 exogenous and endogenous growth. 



The record of this study may consist in a few diagrams 

 and a complete list of the materials studied and statement 

 of what they illustrate. 



Study 22. Spermatophyte development. 



Materials needed : Flowers and flower buds, from which 

 to obtain ripe pollen; sections of female gametophytes ; 

 seeds with and without endosperm. 



Study the pollen grains wet, dry, and germinating in 

 drop cultures. 



Study the enfolding integuments in sections of young 

 ovules (fig. qSp) ; study the mature gametophyte in older 



