Osyris, Loranthus and Viscum. 191 



8ac in Cucurbitaceoe, and more remotely to the processes of the stigmata of 

 Asclepiadece. 



Osyris, independently of the extension backwards of the sac, presents great 

 anomalies in its functions, although, as will be seen, there is a tendency to the 

 same in Santalum. 



Embryo-sacs, whenever they exist, are generally supposed to contain the 

 embryo, and it is in them that all the important changes consequent on fecun- 

 dation take place. In Osyris, however, although the sac has direct relations 

 with the boyaux, no penetration or inflection appears to occur; but the cellu- 

 lar growths are formed, or, as they appear to be, are deposited on its convex 

 surface ; and it undergoes no change, except, perhaps, a greater amount of 

 protrusion, due, I think, to the disappearance of part of the nucleus, and a 

 less amount of adhesion to the cellular mass. Elsewhere, whenever an embryo- 

 sac exists, it enters into the composition at least partially, and very generally 

 entirely, of the seed. In Osyris it does not appear to do so. Osyris is, I think, 

 also very remarkable from the direction in which the embryo appears, which 

 is towards, not, as in Santalum and Loranthus, from the pollen tube, and still 

 more so in its apparent distance from the end of the pollen tube, when attached 

 to the head of the embryo-sac. 



Application of the hoyaux is in Santalum of very general occurrence, but the 

 fertilizing effects are almost invariably confined to one sac. So far as I have 

 examined, there are no appreciable differences between the sacs before fecun- 

 dation, or in the manner or degree of application of the boyaux : on this con- 

 siderable stress may perhaps be laid, as it appears to me to be fatal to the 

 hypothesis of M. Endlicher, who considers the moisture of the stigma as the 

 fertihzing substance ; to that of M. Schleiden, who attributes similar func- 

 tions to the embryonary sac ; and to that of M. linger, who believes that the 

 pollen grains, when they arrive on the stigma, are already fecundated* : all of 

 which speculations truly deserve the name of hypotheses. 



Although my numerous observations have had especial reference to the 

 point, I have not been able to show by direct observations that the vesicle 

 is the end of the pollen tube, but I have no doubt that this may be done. I 

 rely on the evidence furnished me by my friend Mr. Grant as to the absolute 



* Meyen's Report for 1839 on Physiol. Bot., Ann. and Mag. Nat. Hist., No. 43, May 1841. 



