Osyris, Loranthus and Viscum. 197 



the albumen : if they do, it would appear to be, at least in L. bicohr, to an 



inconsiderable extent. 



The relations between the pollen tubes and these sacs in both species appear 



to me very singular. In the first place, the point of entrance is in L. bicolor 



not always single or in the centre ; in the second, the tubes have appeared 



almost invariably to be two ; in the third they do not undergo the ordinary 



changes until they appear to have reached or passed beyond the posterior 



ends of the sacs. On these singular points my limited experience can bring 



nothing to bear. 



4. Origin of the Embryo. 



The first process in the development of the seed, subsequently to the pene- 

 tration or application of the boyau to the embryo-sac, would in Santalum, 

 Osyris, Loranthus and Viscum appear to consist of the formation of cellular 

 tissue. This may be applied, I believe, to most if not to all instances. This 

 cellular tissue appears to have two different origins ; one, and this is the 

 earliest in development, being perhaps referable to the embryo-sac, while the 

 other appears directly referable to the anterior ends of the pollen tubes. The 

 amount of both these tissues may vary considerably ; and it may probably be 

 found that whenever the first is developed in any quantity, the subsequent 

 presence, or rather, perhaps, permanence, of albumen is determined*: the 

 second may be limited to one or to a few cells, forming the funicle or " sus- 

 pensor" of the embryonic mass ; or it may be developed to a great extent, 

 as in Loranthus globosus and certain Gymnospermous plants ; or, as Viscum 

 would seem to intimate, the poUinic vesicle or anterior end of the pollen tube 

 may develope within its interior the proper tissues of the embryo. 



In no instance, perhaps, where the embryo is developed from the ends of 

 the pollen tubes, does it become developed so immediately that no cells inter- 

 vene between it and the end of the pollen tube ; this is particularly evident 

 during the earlier stages of development. 



That part of the embryo in which the condensed tissues occur, and which, 

 from its appearance and frequent tendency to constriction round its base, I 



* Santalum and Loranthus, but especially L. bicolor, seem to me to indicate that the albumen is 

 probably derived from the embryo-sac, which would thus appear to be, at least in some measure, a 

 potential organ. 



2 d2 



