EMBRYO 123 



size, and beginners are apt to mistake it for the embryo : the 

 terminal cell next the embryo (the hypophysis) encroaches 

 between the four lower octants of the embryo. 



3. The octants so divided as to form three layers of cells, 

 which have been distinguished as (a) the external dermatogen, 

 (b} the pcriblem, (c) the central plerome. 



4. The two cotyledons formed by lateral outgrowth from the 

 upper tier of octants, the apex of the radicle derived from the 

 hypophysis, the hypocotyledonary stem from the lower tier of 

 octants. 



5. Other parts as before. The apical bud or plumule formed 

 between the cotyledons. 



ii. Monocotyledon. 



Treat ovules of Alisma Plantago in the same way, and 

 observe the following stages of development : 



1. Suspensor and embryo consist of a single short series of 

 cells, produced by tran verse divisions. 



2. The terminal cell divides longitudinally into four (first 

 tier). 



3. The second, third, and fourth cells from the end also 

 divide successively (second, third, and fourth tiers). 



4. The cells of the body of the embryo divide (as in Capselld) 

 so as to form three layers : (a) external derm ato gen, (b} peri- 

 blem, (c) central plerome. 



5. A lateral depression of the surface, at the level of the 

 second tier. At the basal lip of this the apical cone of the 

 plumule is formed. 



The single cotyledon is formed from the first tier. 



The radicle from the third tier. 



The apex of the root from the fourth tier. 



Compare these results with those obtained in Capsella. 



B. DEVELOPMENT OF THE ENDOSPERM. 



I. This may be traced in the embryo-sac of Caltha palustris 

 in material which has been fixed and preserved in absolute 

 alcohol or strong methylated spirit : it is an advantage 



