THE MEGASPORANGIUM 



57 



tion becomes more pronounced and takes the form of a backwardly 

 directed process (Fig. 40D-G) which resembles an aril in later 

 stages. A very peculiar condition occurs in Opuntia (Archibald, 

 1939), where the extremely long funiculus completely surrounds the 

 ovule and looks like a third integument (Fig. 39). 



D E F G 



Fig. 40. Diagrams of ovules showing origin of aril or third integument (A-C) and 

 caruncle (D-G). A,B, Asphodelus fistulosus. (After Stenar, 1928.) C, Trian- 

 thema monogyna. (After Bhargava, 1935.) D, Brachychilum horsfieldii. (After 

 Mauritzon, 1936.) E, Burbidgea scMzocheila. (After Mauritzon, 1936.) F,G, 

 Careya arborea. (After Mauritzon, 1939.) 



Whatever may be the condition of the integuments in the younger 

 stages, they often present a very different and a more complicated 

 aspect in the mature seed. Frequently several layers of cells are 



