55 



round and down near the chalaza. This is caused 

 by one side of the ovule growing faster than the 

 other ; 



anatropous, when they are completely inverted. The 

 chalaza and the micropyle are in the same straight 

 line, but the upper part of the funicle is apparently 

 adherent to the side of the ovule and forms a ridge 



O 



called the raphe. 



Intermediate forms between the above types of course 

 occur. 



The spot where the end of the funicle is joined to the ovule 

 is called the hilum. When the ripe seed separates from its stalk 

 a scar marks the position of the hilum. In orthotropous and 

 campylotropous ovules the hilum and chalaza coincide ; in 

 anatropous ovules they are at opposite ends of the ovule. 

 When the raphe is turned towards the ventral suture of the 

 carpel it is said to be ventral and when turned towards the 

 dorsal suture it is dorsal. In the nucellus of the ovule there is 

 a large cell called the embryo-sac, containing protoplasm which 

 is more or less divided up into separate da lighter- cells which 

 may, or may not, be provided with delicate cell-walls. When 

 a ripe pollen-grain reaches the sticky, surface of the stigma it 

 germinates. Its outer coat is burst and a long delicate tube is 

 sent out, called the pollen-tube into which pass the proto- 

 plasmic contents of the pollen-grain. This tube penetrates 

 the tissue of the stigma, and of the style if there is one, usually 

 enters the micropyle and grows until its tip comes in contact 

 with the apex of the embryo-sac. A portion of the protoplasm 

 then passes out from the pollen-tube and unites with a part 

 of the protoplasm in the embryo-sac, and with the fusion of 

 these separate masses of protoplasm into one fertilisation is 

 completed. The lump of protoplasm surrounds itself with a 

 cell-wall, begins to divide, and develops into the so-called 

 embryo, or young plant, the ovule now having become the 

 seed. 



52. Having completed our Types O r 



examination of the parts of the flower a few points which Flowers 

 may cause difficulty remain to be noted. 



In cases where some of the floral parts are suppressed Difficulty, 

 and not developed, it is not always easy to decide on the true 

 nature of the parts which are present. Thus in the flower of 

 Clematis, there are usually 4 conspicuous leaves which look 

 like petals, but which are really sepals, no petals being develop- 

 ed. This is indicated by the fact that rudimentary petals are 



