V] POLLINATION AND FERTILISATION 73 



deeply enveloped in protective coverings. The usual 

 isolation of the pollen-grain allows of its free transfer, 

 and the varied mechanisms of flowers secure that the 



Fig. 15. Ovai-y of Polygonum convolvulus during fertilisation, fw — 

 wall of ovary : fs = stalk-like base of ovary : fu = funiculus : cha = 

 chalaza : m^ = nucellus : mi = raicropyle : // = inner, ?> = outer 

 integument : <3 = embryo -sac : efc = central nucleus of embryo-sac : 

 ei = egg-apparatus : an = antipodal cells : g = style : n = stigma : p = 

 pollen-grains: _/96 = pollen-tubes, (x48.) (After Strasburger.) 



