192 



CA8SELL'S POPULAR GARDENING. 



In this embryo-sac are suspended three masses of 

 protoplasm (not shown in the woodcut), each with a 

 nucleus. One of these three is destined to become 

 the egg-, and may be called the germ, or " oosphere ;" 



Fig. 85.— Fertilisation of tlie Ovule, showing the passage of 

 the PoUeu-tuhes from the Stigma to the Ovules. 



the other two are called " s^mergides," a word for 

 which no English equivalent has yet been found. 

 Their use will be mentioned later on. At the other 

 end of the embrj^o-sac are three minute cells, each 

 with a nucleus; these are the "antipodal cells," 

 which in this place we may dismiss with the mere 

 mention, as their relation to practical matters is only 

 remote. The contents of the embryo-sac (other than 

 the oosphere) are supposed to correspond to a pro- 

 thallus, such as exists in some Cryptogams. The 

 nucellus of the ovule, with its embryo-sac, containing 

 oosphere, synergides, and antipodal cells, is equipped 



for work when stimulated by the arrival of the pollen- 

 tube and its contents. 



The pollen-tube travels down the style, as we have 

 seen, worms its way along the stalk of the ovule, 

 enters the micropyle, akeady referred to (Figs. 86^ 

 87), and comes into contact with the embryo-sac. 



Formation of the Oospore, or Egg.— 



Then happens a remarkable series of changes, 

 eventuating in the formation of the egg, as we may 

 call it, and the embryo plant derived from it. The 

 changes in question, so far as known, may briefly be 

 described as the passage of the end of the poUen- 

 tube, with its nucleus and protoplasmic contents, 

 into one of the " synergides " — in other words, the 

 protoplasm of the pollen-tube and that of the synergid 



the Micropyle, and 

 Fig. 86. — An Ovule with a Pollen-tube peue- 



Pollen-tube entering the trating the Embryo- 



Micropyle (magnified). sac. 



mix, and the nucleus of both disappears, the one 

 entirely, while the other is temporarily disintegrated. 

 The synergid now has a uniformly granular com- 

 position, and an irregularly lobed form. One or 

 more of these lobes come into contact with the germ, 

 or oosphere, which, like the synergid, has up to this 

 time been a mere mass of protoplasm enclosing 

 a nucleus ; but the oosphere now, after contact and 

 fusion with the sjTiergid, develops a cell- wall, and a 

 second nucleus becomes apparent. This second 

 nucleus is supposed to be derived originally from 

 the pollen-tube, to be broken up, or diffused, as 



