EMBRYO 211 



of cells, which have been distinguished as (a) the ex- 

 ternal dermatogen, (&) the periblem, (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 transverse 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 divided (as 

 in Capsella) so as to form three layers: (a) external 

 dermatogen, (&) periblem, (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 



P 2 



