404 DEVELOPMENT OF OVULE. [BOOK i. 



extensions will be found to have reached nearly to the base 

 of the placenta. Their terminations in this direction are in 

 culs de sac ; there is a tendency to division and irregularity 

 of outline of all the included part, not even excepting that 

 within the ovule itself. The contents seem, with the excep- 

 tion of the part within the ovule, to be chiefly grumous 

 matter." A similar structure was observed in other plants. 

 In Osyris the ovule is reduced to a nucleus and embryo- 

 nary sac, which is prolonged in the same directions as in 

 Santalum, but not to such a degree beyond the apex of the 

 nucleus. In Viscum the modifications appear to be two : in 

 the one an evident cavity exists in the ovary, and the ovule 

 seems to be reduced to an embryonary sac hanging from 

 one side of the base of a nipple-shaped or conical placenta. 

 In the other the ovule is reduced to an embryonary sac, but 

 this is erect, and has no such obviously distinct point of 

 origin as in the first. The gradation of structure appears to 

 be tolerably complete. One modification of Viscum, in the 

 opinion of Mr. Griffith, tends to show that in Santalum the 

 first steps towards the disappearance of the usual nucleus 

 take place ; Osyris seems to indicate that a similar tendency 

 may affect the embryonary sac; and Santalum appears to 

 allude to a reduction in the embryo sac to the form of that 

 of Osyris. 



The manner in which the ovule is gradually developed has 

 been frequently described, but by no one with more exactness 

 than by Brown in Rafnesia. This botanist says : 



" The first perceptible change taking place in the papilla 

 (which all ovules resemble at their earliest appearance) 

 is a slight contraction at its summit, the upper minute 

 contracted apex being the rudiment of the nucleus. Imme- 

 diately below this contracted portion a dilatation is soon 

 observable, which, gradually enlarging and becoming slightly 

 hollowed, forms a cup in which the nucleus, also proportion- 

 ally increased in size, is partly immersed. This cup, the 

 rudiment of the future integument, continues gradually to 

 enlarge, until it completely covers and extends considerably 

 beyond the nucleus, but without cohering with it. If a 



