THE MEGASPORANGIUM 57 



original angiospermous ovules were straight. The campylotro- 



pous ovule, in which the whole body of the ovule curves, is the 

 rarest type, among Monocotyledons characterizing the Grami- 

 neae, Scitamineae, etc., and among Dicotyledons the Cheno- 

 podiaceae, Caryophyllaceae, Cruciferae, Capparidaceae, Reseda- 

 ceae, etc. These families are more or less specialized members 

 of their alliances, and none of them belong to the Sympetalae. 

 By far the most common form of ovule is the anatropous, and 

 although it is extensively displayed among Monocotyledons and 

 Archichlamydeae, it is present almost without exception among 

 the Sympetalae, and may be regarded as the most highly spe- 

 cialized type of ovule. In its development an anatropous ovule 

 i- at first straight or nearlv so, but very earlv develops a curva- 

 ture at a level with the origin of the first or only integument. 

 As the integuments grow the curvature increases, and usually 

 before the outer integument is complete the nucellus is inverted 

 against the funiculus (Fig. 21). For this reason, in anatropous 

 ovules with two integuments the outer one is not developed on 

 the side toward the funiculus. In abnormal material of Salix 

 petiolaris both anatropous and orthotropous ovules have been 

 observed in the same ovary (Fig. 6). 



The archesporium, as in the microsporangia, is recognized 

 bv the increasing size and the different reaction to stains of one 

 or more hypodermal cells. Doubtless all of the hypodermal 

 cells are potentially arehesporial, and there is reason for be- 

 lieving that the deeper cells of the nucellus, most of which are 

 probably derivatives from the original hypodermal layer, may 

 be also. In the vast majority of cases, however, only cells of 

 the hypodermal layer show those changes that are character- 

 istic of arehesporial cells. It is not always easy to determine 

 just how many hypodermal cells are to be included in the ar- 

 chesporium, for there is often complete gradation from cells 

 with the size and staining reaction of undoubted arehesporial 

 cells to those showing neither increase in size nor the character- 

 istic staining reaction. This is to be expected in case all the 

 hypodermal cells are potentially arehesporial, and there is no 

 definite point in its history when such a cell ceases to be merely 

 hypodermal and becomes clearly arehesporial. For this reason, 

 the number of cells recorded as constituting; the archesporium 

 in many plants can not be regarded as precise, but as approxi- 



