398 BOTANICAL GAZETTE [December 



fore forms a band completely surrounding the head at that level, 

 but because the upward projections of the styles unite closely 

 with the head, the stigma is accessible only through the alar 

 chambers, corresponding to the intervals between the stamens. 

 The conductive tissue lines the canal to its end. 



In the formation of the ovules rounded projections {^fig. 2g) 

 are pushed out in longitudinal rows, the lowest in each row being 

 the oldest. Before there is a distinct differentiation of funiculus, 

 one of the h^^podermal cells at the upper outer angle of the 

 ovule can be recognized by its larger nucleus and different stam 

 as an archesporial cell {fig. 2q). Occasionally one finds two or 



m 



three archesporial cells side by side {fig^jo), but in such cases 

 one seems to outgrow the others, for in no case was more than 

 one in its later well developed stage {fig. ji) found in the' same 

 ovule. The epidermal layer over the archesporial cell is the only 

 sterile part of the nucellus. Schacht (lo) figures a nucellus 

 projecting from the ovule like a papilla. Such forms I could 

 not find in A. Cornuti^ and they must be exceptional. By the 

 cessation of growth in the nucellus, and its continuation around 

 it to form the single integument, the nucellus comes to appear 

 deeply sunken {fig, J4), The nucellus is short lived, being very 

 soon replaced by the embryo sac. It seems remarkable that 

 there should be no nucellus or integument in Cynanchum as 

 reported by Chauveaud. If one takes the view that he over- 

 looked an evanescent nucellus his story accords well with that 

 in Asclepias and Acerates, his *' revetement protecteur tres epais 

 becoming the integument. Its appearance and manner of forma- 

 tion are about the same as the integument of the genera studied 



The archesporial cell reaches a size equal in section to 



a 



dozen of the surrounding cells. No parietal (tapetal) cell is 

 cut off, and by two successive divisions a row of four megaspores 

 is formed {figs. J2,jj). This does not always occur during the 

 same stage in the development of the integument, as sometimes 

 it occurs when the nucellus is not yet covered, and at other 

 times when the nucellus is deeply imbedded in the body of the 

 ovule. To avoid confusion the two cells resulting from the first 

 division of the archesporial cell will be called daughter cells* 



