_ 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. Allemäo is, that although the “bolbo radicular” is always 
the main growing point of the radicle, he observed in Luphorbiacee, 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 (Cerato- 
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 indieation 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, Urtica, Senecio, 
Sonchus, Calendula, Matricaria, Veronica, Phaseolus, Medicago, &e., although it is not 
of general occurrénce. In the singular mode of germination of the seeds of Tropeolum, 
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. Allemäo 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 " 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 —5 
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 "e is shown Ww begin from 
its sprouting point, called by Dr. Allemäo the “ bolbo radicular,” or“ gommo. This yy 
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 € 
by numberless facts, and more especially by one to which I lately called the atten seas 
the Linnean Society, the germination of the embryo of Xanthochymus, as SRM t 
Roxburgh, where, in addition to the principal root thrown out at the base of the : a 
the point which Dr. Allemáo would call the radicular bulb, another secondary root is 
seen sprouting from the summit of the nucleus, out of the ascending collar or ee = 
mediately below the scales which appear to be the minute cotyledons, showing that the 
