182 Mr. Griffith on the Ovulum of Santaluin, 



conversion into the embryo. (Tab. XXI. fig. 9.) And this is I think its only 

 anomaly, that is, comparing it with Santalum, and more especially with Loran- 

 thus*. 



In connexion with these details, I venture to remark on the following 

 points : — 



1. Solidity of the ovarium, and the appearance of the ovulum after fecun- 



• My paper on Viscum appears, I am sorry to say, to have been generally misunderstood. In a 

 letter dated April 1839. M. Decaisne states that the development of the ovula of Viscum album is like 

 that I had described as occurring in Loranthus, and that the development of the same part in the 

 Mergui Viscum appears identical with that of Thesium. In the translation of his memoir on Mistletoe, 

 it is said that in that same species three ovula are detected in each cell on a central support. 



These discrepancies are by no means confined to the ovulum ; they extend to the fibrous covering of 

 the seed. 



It appears to me that the only similarity in our observations is to be found between Santalum and 

 Thesium ; for the whole of his observations on the female parts of Viscum album differ from those which 

 I made on a tropical species of the same genus. Between M. Decaisne's inferences and my own there 

 is little analogy ; for while, according to him, V. album presents no anomaly in its ovulum beyond re- 

 eduction to a nucleus, I was led to the conclusion that the anomalies, affecting this genus, at least as 

 exemplified by the Mergui species, are of a more remarkable nature. 



When I was occupied in 1 834-35 by the structure of Viscum, the question of the nature of the part, 

 which I called nipple- shaped process, had occurred to me, although in my account I did not enter into 

 any detail regarding it. My assumption of its being rather analogous to a placenta was founded on 

 the eccentricity of the sac, which I consider the sac of the embryo. 



I knew of no instance in which the embryo sac had not a definite relation to the axis of the nucleus, 

 or in which it arose from the surface of that body. I therefore described the part in question as a 

 nipple-shaped process, avoiding, in the imperfect state of my knowledge, all speculation as to its nature. 

 Although a good deal dismayed by my blunders regarding the solidity of the ovarium of Loranthus, 1 

 am still inclined to adhere to the other inferences therein contained : for although in the description of 

 fig. 5. (by mistake 4.), Tab. X., vol. xviii., it is inadvertently stated that the ovulum is reduced to a 

 nucleus, what I believe to be its true nature is elsewhere distinctly alluded to. 



The structure of the Mergui Viscum, as there detailed, is an obvious approach to that oi Santalum. 

 And I should not be surprised, from my greater experience of Santalum and acquaintance with Osyris, 

 if it be found to approach so closely as to differ in little except in the absence of a nucleus ; the con- 

 stant browning of the tissue of the placentae along the line of the posterior extension of the embryonary 

 sacs in those genera leading me to suspect that something of the same nature occurs in Viscum. The 

 occurrence of two such dark lines with the development of only one sac still further points out the im- 

 portance of studying every species of this genus : for this would seem to indicate the existence of the 

 sacs or tubes in the placentae prior to their exsertion ; a fact of considerable importance, and one which, 

 if established, would considerably modify my ideas of the nature of these particular placentse. 



