STRUCTURE.] LAW REGARDING PLACENTAE. 373 



but particularly in such as, habitually having but one carpel, 

 occasionally form two, as the Wistaria sinensis, Alchemilla 

 arvensis, Cerasus acida, &c. ; in these the second carpel, 

 when added, does not arise by the side of the first, but 

 opposite to it, the face of its placenta being in front of that 

 of the habitual carpel. A fourth proof of this usual direction 

 of the placentae towards the axis is afforded by those pistils 

 in which a great number of carpels is developed in several 

 rows, as in the Strawberry and the Ranunculus : in all these 

 the placentae will be, without exception, found directed 

 towards the axis, and consequently towards the back of 

 every row, except the inner. For example, in the following 

 diagram (123.), let o be the axis, b b placentae, c c the backs 



fig. 123. 



of carpels ; the placentae, b b, of the inner row will be next 

 the centre o ; the placentae, b b } of the second row will be 

 next the backs, c c, of the first row ; and so on. 



fig. 124. 







OSO3 



If the order of development of leaves were exactly followed 

 in that of the stamens and carpels, it would happen that the 



