THE MEGASPORANGIUM 55 



Umbelliferae being the most notable exception. On the other 

 hand, a single integument is characteristic of the ovules of the 

 Sympetalae, as well as of the Umbelliferae, and some other 

 Archichlamydeae, such as species of Ranunculus, Legmninosae, 

 etc., the integument being very massive and in comparison with 

 the very small nucellus constituting the bulk of the ovule. 

 There seems to be every indication that two integuments are 

 characteristic of the ovules of the more primitive Angiosperms ; 

 that they persist among Monocotyledons even among the most 

 highly specialized families ; but that among Dicotvledons thev 

 are replaced in the higher groups by the single massive integu- 

 ment. The fact that the single integument is more massive 

 even than both integuments when there are two suggests that it 

 represents two integuments in the sense that their primordia 

 are no longer differentiated. This is very far from meaning 

 that two integuments have fused to form the single one, but 

 that a single integument is developed by the same region that 

 in other cases produces two. 



Certain exceptional cases in the development of integu- 

 ments may be noted. Among the Loranthaceae and Balano- 

 phoraceae no integuments are formed ; and the same claim is 

 made by Chauveaud 2i ' 65 for Cynanchum (Asclepiadaceae), 

 perhaps to be explained by Asclepias (Frye 66 ), in which the 

 integument might be mistaken for part of a naked nucellus. 

 The same claim is made for Santalaeeae, and it may be true 

 of most of them; but in Myzodendron punctulatum Johnson 22 

 has described a single-layered integument that does not cover 

 the free end of the embryo-sac. This suggests an abortion 

 of the integument, which in other members of the family 

 may not have been recognized or may even have been sup- 

 pressed. The ovule of Houstonia is said by Lloyd 61 to have 

 no integument. The ovule of Hippuris long had the reputation 

 of having no integument, as reported by Schleiden, 1 Unger, 2 

 and Schaeht. 3 In 1880, however, Fischer 15 in reinvestigating 

 it discovered that a single integument is formed, but closes over 

 the nucellus so tightly as to give the appearance of a naked 

 nucellus. Oliver 21 discovered exactly the same behavior in 

 his new genus Trapella, except that the integument is very 

 massive. The same thing has also been observed by !Murbeck " 

 in the parthenogenetic Alchemilla alpina, in which the single 



