50 



MORPHOLOGY OP ANGIOSPBEMS 



phora, suggests the explanation. Lotsy finds that the enlarged tip 

 of the flower axis soon completely fills the cavity of the ovary, 



and that one or more hypodermal 

 cells of this axis form the mega- 

 spores (Fig. 20). This is exactly 

 the case of Loranthus, and suggests 

 that in the allied Balanophora the 

 same " mamelon " is present, but 

 with no carpellary investment, the 

 naked nucellus ( as the " mamelon " 

 would seem to be in this case ) de- 

 veloping the remarkable neck-like 

 outgrowth of sterile tissue. In both 

 families it seems certain that the 

 megasporangia are cauline. 



Foliar ovules are related to the 

 carpels in a variety of ways. By far 

 the most common position is for the 

 ovules to arise in a line along each 

 side of one of the two prominent vas- 

 cular bundles of the carpel, a very 

 common position for the sporangia 

 of ferns. In the older morphology 

 this line was thought to represent the 

 abutting margins of the infolded car- 

 pellary leaf, and hence such ovules 

 were called " marginal." In fact, 

 this double line of ovules, ami the 

 dehiscence of many carpels along it, 

 seemed to the supporters of meta- 

 morphosis to prove the foliar nature 

 of the carpel. As might be expected 

 from the behavior of sporangia in 

 ferns, there are cases in which mules 

 arise without such close connection 

 with a prominent vascular bundle. For example, in Butomus, 

 Nymphaea, Nuphar, Obolaria, Barionia, and many species of 

 Gentiana, the ovules arise from the whole inner surface of the 

 carpel. In the older terminology these were called " super- 

 ficial " ovules, and associated with them, curiously enough, were 



B 



Fig. 19. — Loranthus sphaerocarpus, 

 A, longitudinal section of a young 

 flower showing the "mamelon" 

 (m) ; x 25. -Z>, longitudinal sec- 

 tion of a u mamelon " at a later 

 stage showing two hypodermal 

 archesporial cells; x 300. — After 

 Tbeub.'s 







