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. Ovary of Polygonum convolvulus during fertilisation, fw = 

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

 cbalaza : rm:=nucellus : mi = micropyle : u = inner, ie = outer 

 integument : e = embryo-sac : ek = central nucleus of embryo-sac : 

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

 pollen-grains : ps = pollen-tubes. (x48.) (After Strasburger.) 



