VESSELS IN MONOCOTYLEDONOUS AND DICOTYLEDONOUS PLANTS. 265 



vessels in the plumule and cotyledons, with the descending system of dotted vessels in the 

 radicle, as distinguished in the germinating embryo of the common French Bean. 



Another fact related by Dr. Allemao is, that although the " bolbo radicular'''' is always 

 the main growing point of the radicle, he observed in JEupliorbiacece, four other cruciform 

 branches on one horizontal plane, proceeding from this radicle. This fact is not novel, 

 for it was noticed more than forty years ago by St. Hilaire (Ann. Mus. xix. 468), where 

 he describes the same feature in the germination of a Ranunculaceous plant (Cer oto- 

 cephalus) : here the main shoot is shown, growing in the ordinary way of an exorhizal 

 root, but four other branching rootlets are produced on one plane, from the collar of its 

 young root, which make their appearance through lacerations of the external tunic : their 

 earliest indication is in the form of tubercles, through the investing covering of which 

 these rootlets burst a passage, in all respects like the coleorhiza observed in the germi- 

 nating embryos of monocotyledonous plants, so that, although the main root here is 

 exorhizal, the secondary rootlets are distinctly coleorhizal. This coleorhiza is sometimes 

 extended to some distance, along with the rootlet ; but in other cases it forms merely an 

 areola around its base. St. Hilaire observed the same appearance in the growing embryos 

 of numerous other exorhizal plants, as those of Plantago, Valerianella, TJrtica, Senecio, 

 Sonchus, Calendula, Matricaria, Veronica, Phaseolus, Medicago, &c, although it is not 

 of general occurrence. In the singular mode of germination of the seeds of Tropceolum, 

 the radicle, though exorhizal, exhibits a kind of valve-like opening for the exit of the 

 plumule, which has been called a coleorhiza : a somewhat similar appearance is said also 

 to occur in the germination" of the seed of Viscum album, but that I apprehend can refer 

 only to the coleorhizal mode of bursting of the attenuated expansion of the thin covering 

 of the albumen which is spread over the growing radicle. 



Dr. Allemao here considers the radicle of the embryo as part of the caulicle or stem, 

 and the root as originating in the subsequent growth of the embryo, after it is released 

 from its integuments, and produced by the expansion of the obtuse extremity of the 

 radicle, which he calls the " gommo," and Gaudichaud the " radicular bulb." This view 

 was also taken by Turpin nearly twenty years ago, and is figured as such in the germina- 

 tion of Solanum tuberosum, where all the radicular portion of the embryo is considered 

 as the tigelle, or part of the ascending system, while the true root is shown to begin from 

 its sprouting point, called by Dr. Allemao the " bolbo radicular" or " gommo." This idea, 

 though supported by some, has not been much countenanced, and I do not perceive the 

 advantage of this theory over that more generally received, which assigns to the radicle 

 the function of the elementary root, its commencement being at the point of union of the 

 cotyledons and their junction with the plumule. The contrary hypothesis is disproved 

 by numberless facts, and more especially by one to which I lately called the attention of 

 the Linnean Society, the germination of the embryo of Xanthochymus, as figured by Dr. 

 Roxburgh, where, in addition to the principal root thrown out at the base of the seed, at 

 the point which Dr. Allemao would call the radicular bulb, another secondary root is 

 seen sprouting from the summit of the nucleus, out of the ascending collar or tigelle, im- 

 mediately below the scales which appear to be the minute cotyledons, showing that the 



