1578 



A TEXTBOOK OF THEORETICAL BOTANY 



The testas of such seeds are usually papery and the endocarp is the true 

 protective structure. Among the simplest devices are those in which the 

 endocarp splits into two halves, as in Primus (single carpel) or Jiiglans 

 (two carpels). In these cases a definite plane of cleavage is formed before- 

 hand and the shell is forced open by the swelling seed inside. In Cocos 



i ''^Z. 





Fig. 1438. — Cocos uttcifeid. i, 2 and 3. Male ami 

 female flowers. 4. Germinating fruit. The 

 cotyledonary haustorium has enlarged to fill 

 nearly all the hollow space surrounded by the 

 layer of endosperm. (After Bailloti. From Lotsy, 

 "Vorlrdi^e L'her Botnnische Staniifiesgeschic/ite".] 



there is no special opening, but one of the three round depressions at one 

 end of the shell is unlignified and through this the seedling forces its way 

 out. A more advanced device is the provision of a special portion of the 

 endocarp, a kind of shutter or fenestra (Fig. 1440) which is readily pushed 

 open from inside like a valve, e.g., Nyssa (one seeded), Cormis (two seeded) 

 and Tecto?ia (four seeded). A further device is that of an aperture closed by 

 a stony plug which is pushed off by the seedling, e.g., Sclerocarya (Anacar- 

 diaceae) (Fig. 1441). Pleiogynium, another genus of the same family, has 

 up to twelve seeds in each fruit and has a stony mesocarp in addition to the 



