52 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



tegmen or inner integnment, and the testa or outer 

 integument of the seed. The j)ortion of the seed 

 dispersed may therefore be — 



7. The nucleus enclosing the embryo. 



8. The nucleus enveloped by the tegmen : Oxalis. 



9. The complete seed. 



In like manner the body dispersed may include 

 part of the fruit. • The seed may be enclosed in — 



10. The endocarp : drupaceous and stone-fruits. 



11. The endocarp and mesocarp. 



12. The entire pericarp. 



In this last case the fruit rather than the seed is 

 dispersed. Even the fruit is sometimes accompanied 

 by accessory j^arts— calyx, corolla, receptacle, etc. ; 

 while in splitting-fruits the seed is enclosed within 

 a section only of the fruit. 



In every sx>ecies of plant there is i^roduced one 

 set of bodies intended for distribution. This is 

 sufficient where no necessity exists for fertilisation. 

 So long as continued vegetative reproduction does 

 not lead to degeneration, the perpetuity of the 

 species may be secured by the distribution of one 

 set of germs. But when the necessity arises for 

 sexual reproduction, the arrangements for distribution 

 become more comx^licated. In general, we may 

 assume that where true sexuality exists a twofold 

 disiDersion is requisite or at least advantageous. In 

 the hrst jilace, the male element or sperm cells 

 must be so disseminated as to insure the fertilisation 

 of as many germ cells as possible. Secondly, pro- 

 visions are required for the dispersion of the 

 fertilised germs. 



When the problem is thus stated it will be seen 

 at a glance that the dispersion of the male element 

 (antherozoid, microspore, or pollen-grain, as the case 

 may be) is of greater urgency than even the 

 distribution of the fertilised germs. Accordingly, 

 we iind that the contrivances for distributing the 

 male cells are, on the whole, far more perfect than 

 the arrangements for dispersing the products of 



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