A^'GIOSPERMM 167 



formed. The latter, increasing rapidly, fills the embryo-sac, 

 and, besides, encroaches on and displaces, in most cases, the 

 surrounding tissue. It is then more or less completely 

 consumed in the further development of the embryo. 

 After a many-celled body is formed at the lower end of 

 the suspensor, or proembryo, partitions then arise in the 

 cells, parallel to the surface ; and thus is formed the pri- 

 mary epidermis, or dermatogen. Simultaneously with this, 

 there is also, as a rule, a differentiation of the inner cells 

 foreshadowing the future tissue systems. A little later, 

 either a depression in one side of the thallus-like structure 

 is formed, which becomes the punetum vegetationis of the 

 embryo, and the apical part extending beyond this point, 

 the single cotyledon (Fig. 148) ; or instead, the apical 

 point of the embryo becomes the punetum vegetationis, 

 which is enclosed between the two cotyledons that grow 

 out symmetrically from opposite points below, and adja- 

 cent to the same. 



i86. The growing embryo, embedded in the nutrient 

 endosperm, increases in size at the expense of the latter. 

 •In many cases it ceases its growth before all the endosperm 

 is absorbed ; as in the Crowfoots (Hanunculacea), Violets 

 (^Violacece), Palms {Palmaeeos), Grasses {GraminecB), etc. 

 Such seeds were formerly designated by the term albumin- 

 ous. Otherwise, the embryo grows till it has absorbed and 

 displaced the whole endosperm, storing its nutrient sub- 

 stances in the much enlarged cotyledons, as in the Mustard 

 family (Oruciferw), the Roses (^Eosacece), the Oaks (Cupu- 

 liferce), etc. Seeds containing such an embryo were called 

 exalhuminous. It happens in a few cases, for example, in 

 the Water-Lily family (Nymphacece), that the endosperm 

 is only slightly developed; in such cases the nutriment 



