88 Mr. J. Miers on the Tribe Colletiese, 



of the integuments of the seed, which I have invariably found in 

 one unbroken continuity, was therefore not fully traced by that 

 eminent botanist, although it is evident, from the above quota- 

 tion, that he had noticed the return of the raphe over the cha- 

 laza, and its partial descent down the contrary face of the seed. 

 It is strange that this remarkable and novel feature was not 

 afterwards alluded to, and that the mention of this extension of 

 the tracheal vessels is omitted in the very copious diagnosis he 

 gives of the order, where every other circumstance connected 

 with the structure is carefully enumerated. 



Some indications, leading to a knowledge of the origin of the 

 external crustaceous envelope of the seed in Rhamnacea may 

 probably be drawn from Brongniart's valuable memoir above 

 quoted, in which he records the changes which he observed 

 during the periods of the impregnation and growth of the ovule 

 in that family. These details were published in 1827, a year or 

 two prior to the appearance of MirbePs two celebrated memoirs 

 on the development of the vegetable ovule, and before the mo- 

 dern nomenclature of the parts of the ovule and seed was 

 adopted. I will therefore briefly recapitulate such of his obser- 

 vations as bear upon the subject under consideration. He 

 noticed* that the stigmatic tissue terminated in a small cellular 

 protuberance (since denominated the "telse conductrices ") in 

 the inner angle of the cell of the ovary, close to the foramen of 

 the anatropous ovule; and he remarked the condition under 

 which the latter became fecundated : the ovule is always sup- 

 ported upon a somewhat elongated funicle filled with nourishing 

 vessels, and surrounded by loose cellular tissue; this funicle, 

 which is very contracted before impregnation, begins to swell 

 from the moment that the stigma has received its fertilizing 

 influence; it afterwards expands and extends itself over the 

 foramen of the ovular tunic. Brongniart, who first traced the 

 expansion of the boyaux of the pollen-grains, and their passage 

 down the stigmatic channels f, was not then aware of their ulti- 

 mate extension through the prominence he observed at the 

 termination of those channels ; nor did he notice the continuity 

 of one of these boyaux with the minute thread which he had 

 remarked in connexion with the embryo- sac, and which he con- 

 sidered to be an emanation from its neck : according to the 

 notion he then entertained, he concluded that the act of impreg- 

 nation was conveyed through the agency of the cellular tissue 

 of the umbilical cord J, which the fact he recorded of the swell- 



* Ann. Sc. Nat. x. 340. 



t Ib. xii. 152 & 256; read before the Academy Dec. 26, 1826. 

 J Ann. Sc. Nat. x. 343 : "Et c'est par 1'intermediaire de ce tissu cellu- 

 laire du cordon ombilical que je pense que s'opere 1'impregnation de 



