GROUP IV. PHANEROGAMIA. 



439 



simply grows and becomes the macrospore without any special 

 differentiation. However, in the Cycadacese, the wall of the 

 mother- cell undergoes that differentiation which is characteristic 

 of spores, so that the wall of the macrospore consists of two 

 layers the outer of which is cuticularised. The macrospore is 

 simply a large cell, containing vacuolated protoplasm in which 

 lies a nucleus, and having, as a rule, a wall of cellulose. 



FIG. 285. Torenia asiatica. A Two anatropous ovules on the placenta p ; e apex of 

 embryo-sac projecting beyond the micro pyle; e* its broad chalazal end in the ovule; 

 /funicle; i integument ( x 240). JB and C Free apex of embryo-sac, with egg-apparatus, 

 before fertilisation ; fl caps of the synergidae ; o oosphere. D and E The process of fertili- 

 sation ; t the pullen-tube ; / part of the funicle ( x 600 : after Strasburger). 



In the course of its growth, the macrospore frequently causes 

 the absorption of more or less of the tissue of the nucellus, more 

 especially towards the micropylar end. It commonly attains 

 such a size that little or none of the nucellar tissue remains, and 

 it may even project beyond the micropyle {e.g. Santalum, Torenia 

 asiatica, Fig. 285) ; and in many gamopetalous Dicotyledons it 



