THE MEGASPORANGIUM 



51 



the occasional cases in which the ovules arise from the other vas- 

 cular bundle (the " midrib " of the infolded leaf theory), as in 

 Brasenia, Cabomba, and Astro car pus (Eichler, 8 2: 17). Ac- 

 cording to Warming 7 a third category is necessary to include 

 such cases as Zannichellia, Ranunculus, and Sedum, in which 

 he says the ovules are " basal or axillary." 



The general conclusion seems evident that ovules may arise 

 from any free surface within the cavity of the ovary, whether 

 it be morphologically carpel or axis ; and further, that if the 

 cavity of the ovary becomes obliterated by the enlarged tip of 



A 



Fig. 20. — Rhopalocnemis pJialloides. A, longitudinal section through the "mamelon" 

 before the appearance of archesporial cells. £, later stage showing the two mega- 

 spore mother-cells which develop directly into embryo-sacs, x 116. — After Lotst. m 



the axis, as probable in Loranthaceae and Balanophoraceae, 

 megasporangia arise from the hypodermal cells of the axis 

 without the definite organization of ovules. 



The morphological nature of the ovule was much discussed 

 by the older morphologists. According to the theory of meta- 

 morphosis it was necessary to interpret it as a transformation 

 of some one or more of the vegetative members. The most 

 prevalent view was that it is a transformed leaf-bud arising 

 from the margin of the carpellary leaf, as in the well-known 

 case of Bryophyllum ; and ITofmeister claimed that the ovule 

 of Orchis is a trichome because it arises from a single epidermal 



