Osyris, Loranthus and Viscum. 181 



the percursion of the ovula by the pollen tubes ; the existence of at least two 

 distinct types of development in the genus* ; the formation of one mass of al- 

 bumen from the albun)ina of several ovula ; the exteriority, if I may so express 

 myself, of the embryo from the ovulum ; and its concentrated formation. 



§ 4. ViSCUM. 



I have not yet had an opportunity of re-examining a species of Viscum, pre- 

 senting the organization of that from Mergui, on which my first remarks were 

 founded. The examination, however, of two species of another typef, though 

 remarkably different in habit from each other, has satisfied me not only that 

 the reduction in the parts of the ovulum is of the same degree as that occur- 

 ring in Loranthus, but that the ovulum equally exists before fecundation, and 

 that the phenomena consequent on the occurrence of this present little if any 

 peculiarity, even as regards a retardation of the usual effects. 



The circumstances do not now appear to me to present sufiicient variety to 

 induce me to enter into detail, such as I have thought requisite with regard 

 to Loranthus, Santalum and Osyris, particularly as I am not now able to enter 

 into the question of the origin of the sac (ovulum) and the nature of the parts 

 by which it is surrounded. I consider it, therefore, sufficient to state that the 

 ovulum, which I consider to be reduced to an embryonary sac, exists before 

 fecundation as a clavate membranous closed simple sac, containing fluid mat- 

 ter with some grume towards its apex (Tab. XXI. figs. 5 and 6) ; that after fe- 

 cundation has occurred, its apex will be found to present traces of interruption 

 of continuity, and to be occupied partly by a vesicle, which I assume to be de- 

 rived from the inner membrane of the pollen, and to be the " anterior extre- 

 mity" of the pollen tube ; that the changes consequent on the penetration of 

 this consist first in the development of cellular tissue in the sac, being the first 

 step in the formation of albumen (Tab. XXI. figs. 7 and 8), and that this is sub- 

 sequently accompanied with the occurrence of cellularity in the vesicle and its 



* I am not yet certain whether these two types are so far connected with external form as may en- 

 able me to propose more natural subdivisions of the genus than those at present adopted. 



t M. Decaisne in a letter alludes to the possibility of there being two distinct types of organization 

 of the male flowers of Viscum. Reserving this, I can say that there certainly are as regards the female ; 

 and these, I hope; may be of some use in determining subdivisions and species. At present, nothing can 

 be more inefficient than the characters of the species in Decandolle's ' Frodromus.' 



2 B 2 



