180 STRUCTURAL BOTANY 



d. Ovules 



Passing on now to the ovules themselves, we find 

 that the first stages of their growth are like those of 

 the Wallflower, and here also the ovule soon becomes 

 curved. The curvature, however, takes place in a 

 different manner. In the Lily the nucellus and 

 integuments remain straight ; the bending takes place 

 at the chalaza, so that the whole body of the ovule 

 turns through an angle of 180, and so comes to lie 

 parallel to the funicle, with the micropyle directed 

 towards the placenta, which it closely approaches 

 (see Fig. 83). Such an ovule is called anatropous. 

 The difference between this form and the campylo- 

 tropous ovule of the Wallflower, in which the nucellus 

 and integuments are themselves bent, will be evident 

 on comparing Fig. 83 with Fig. 43, p. 117. The 

 anatropous ovule is the commonest form both among 

 Dicotyledons and Monocotyledons. 



In the Lily the second or outer integument does 

 not become closed, but remains widely open, the 

 narrow micropyle being thus formed by the inner 

 integument alone (see Fig. 83). This is common 

 among Monocotyledons. In other respects there is 

 a general agreement between our two types ; in fact, 

 the main points in the development of the ovule are 

 very uniform throughout the great majority of the 

 members of both classes. 



When we come to the origin of the embryo-sac 

 itself, however, there are some differences to note, 

 though they are not characteristic of the two Classes, 



