74 THE STRUCTURE OF FLOWERS. 



gradual elevation of the ovule occurs in Bicinus and other 

 Euphorbiaceous plants. 



Similarly, if we compare the differences in allied genera, 

 as Ranunculus and Thalictrum ; in the former genus the 

 ovule arises at the very base of the carpel, close to its point 

 of attachment to the axis, and remains there. In Clematis 

 and Thalictrum, the marginal cleft of the carpel appears a 

 little more decidedly above the base, so that the ovule from 

 its earliest period is situated somewhat higher up, and by a 

 further development is carried to a yet higher position, and 

 so ultimately becomes pendulous. Exactly similar differences 

 occur between the orders Composites and Dipsaceoe. 



Hence, it would seem that basilar ovules owe their 

 positions to corresponding degrees of arrest of the growth 

 and development of the carpels, and especially of the basilar 

 portions of the carpellary margins. I think, therefore, we 

 may draw the following conclusion, that the particular form 

 of energy which would cause a carpel to emerge out from 

 and be developed freely and entirely from an axis, is more 

 or less potential than actual.* Consequently, it develops 

 the ovule just where that portion of the carpellary margin 

 would have appeared had it been formed ; so that the tissue 

 whence the ovular papilla emerges may be considered to be, 

 strictly speaking, neither axial nor carpellary, but undif- 

 ferentiated merenchyma, and potentially carpellary. 



From a single ovule we may now pass to plurl-OA'ular 

 ovaries. Dioncea gives us an instance where many ovules 

 arise at the base perfectly free from the ovarian wall. In 

 this flower the pistil consists of five carpels, which emerge 

 congenitally out of the axis, first as a circular rim, which 



* It may be noted that it is more actual in Clematis, etc., in that 

 several ovular papillae are produced in genera with pendulous ovules, 

 besides being more elevated in position ; but only one in Ranunculus. 



