18 STUDY OF COMMON PLANTS. 



most frequently a combination of strong arches, by which 

 the danger of crushing is lessened; in part by the hard 

 testa, which sometimes has a compact, polished exterior 

 that resists the entrance of water and germs ; and in some 

 cases by bitter or otherwise distasteful substances stored 

 up in the seed. In addition to these means of protection 

 the embryo is often securely packed in the midst of 

 abundant endosperm, and not infrequently still other pro- 

 vision is made for its safety. 



Microscopic examination of a seed shows the presence 

 of one or more kinds of reserve materials. As a rule, 

 Reserve starch, or some other non-nitrogeneous sub- 



materials, stance, is associated with aleurone or its equiva- 

 lent, thus supplying all the essential food elements. Oil, 

 as a condensed form of food, is largely employed, in small 

 seeds and those that are transported by the wind, since by 

 the use of this material greater lightness, volume for 

 volume, is secured than if starch were employed. Cellu- 

 lose takes the place of starch or oil in the date and some 

 other seeds, which, as Haberlandt has pointed out, are in 

 this way rendered less liable to decay and the attacks of 

 animals during their long period of germination.^ It is 

 also sgen upon the careful study of almost any seed that 

 the reserve materials are so placed as to be ready for 

 immediate use when wanted, either lying in the cells of 

 the emoryo itself or packed closely around it, and there 

 brought into immediate relation with its absorbing tissue. 



Still other physiological adaptations will be apparent as 

 a greater number of seeds are examined and their struct- 

 Other adapta- ^^al peculiarities brought to light. As an exam- 

 tiona. pie may be mentioned the fact that anatropous 



seeds by curving upon themselves during the early stages 



1 Physiologische Pflanzenanatomie, p. 285 et seq. 



