CH. XIIl] STRUCTURE OF OVULE 113 



At the base of attachment a delicate strand of vas- 

 cular tissue enters, and through this strand the water 

 and food-substances necessary to feed the ovule pass : 

 in many cases this strand is carried through a distinct 

 stalk (funicle), in others the ovule is sessile. The region 

 where the strand merges into the base of the ovule is 

 called the chalaza. 



In the nucellus there is a cavity called the embryo- 

 sac, because the new plantlet (embryo) will be formed in 

 it later. 



With these fixed points to guide us, we may now 

 examine a few differences observable in ovules. 



Many have only one integument as in Compositse, &c., 

 or even none as in Mistletoe, &c., and the point has its 

 significance in descriptive botany. 



In many ovaries the ovules are numerous and small 

 (Orchids), or few and large (Bean), or there is only one 

 (Buttercup). 



With respect to the ovary containing it, an ovule may 

 be erect when standing up from the base ; or suspended 

 when hanging from its roof. When the long axis of the 

 ovule is brought at right angles to the vertical it is 

 horizontcd : it is 'pendulous when obliquely suspended from 

 near the top, and ascending when obliquely rising from 

 near the base. 



If we agree that a central line drawn from the 

 micropyle to the chalaza through the axis of the ovule 

 is its longitudinal axis or, shortly, its axis the following 

 technical peculiarities are to be noted. 



The ovule is orthotropous when the chalaza is below 

 and the micropyle vertically above it, e.g. Polygonacece, 

 many Urticacece, Aroidece, Gistacew, &c. 



If the axis is curved, by one side of the ovule growing 

 faster than the other, so that the micropyle is brought 



w. III. 8 



