242 



PLANT LIFE. 



is divided into as many chambers as there are component 

 carpels, and the partition by which the chambers are sepa- 

 rated represents the adjacent parts of the two carpels. Or 

 the carpels may unite with each other at their edges only, so 

 that the line of union is at the outside 

 of the pistil. In this case the ovulary 

 will have a single chamber. In both these 



Fig. 252. — A transverse , _ . ' 



section of the capsule of methods of union the normal number of 



shepherd's purse. The , , 



pistil consists of two chambers 111 the ovulary may be increased 



carpels, at whose united 



edges two placentas are by outgrowths from the carpels them- 



formed carrying the 



ovules (now seeds). The selves, as in figure 252, where from the 



partition from one pla- , 



centato the other is an united edges of the carpels a plate of tis- 



outgrowth (false parti- 



tion) and not part of the sue has grown out to meet a correspond- 



carpel. Magnified about r 



6 diam.— After Bessey. ing one from the other side, so that what 

 should be a one-chambered pistil has become two-chambered. 

 (Compare also fig. 276.) Even simple pistils are subject to 

 such subdivision of their interior (fig. 253). 



Fig. 253. Fig. 254. 



Fig. 253. — Lower half of the pistil of Astragalus canadensis. It consists of only one 

 carpel, but is divided into two chambers by a false partition, an outgrowth from the 

 midrib of the leaf. Magnified several diam. — After Gray. 



Fig. 254. — Two stages in the development of the ovule of the currant. A, a median 

 longitudinal section of a young ovule ; n, the sporangium ; it. inner integument be- 

 ginning to develop as a ring at base of n ; at, the fundament of the outer integument ; 

 in, the mother cell of the megaspores ; B, a similar section of the sporangium alone, 

 older, showing m' , m", m"' , the daughter cells of m ; m'" , only becomes a perfect 

 spore ; m' and m" do not develop further and become destroyed. Contents of cells 

 not shown. Magnified 350 diam. — After Warming. 



340. Ovules. — An ovule consists of a megasporangium 

 partially enveloped by one or two outgrowths from beneath. 



