466 MR. JOHN MIERS ON A NEW GENUS OF THE BURMANNIACEE. 
induced Dr. Hooker to include Mystropetalum in Balanophoraceæ were its habit, its 
valvate tripartite perianth, its stamens placed opposite the lobes of its border, and 
its extrorse anthers, in all which characters that genus equally resembles Triuris 
and Soridium : these, however, differ in their dicecious flowers and numerous ovaries. 
Were the Cynomoriacee separated from Balanophoraceæ, as above indicated, they need 
not on that account be excluded from the Rhizogens, or merely because of the presence 
of albumen in their seeds, especially as our present knowledge seems to show that the 
organ which has been called their embryo consists of an aggregation of sporule-like 
granules similar to those which we find in all the other orders of this class of plants. 
In order to know the limits of the Rhizogens as a peculiar class, it is desirable to in- 
vestigate the circumstances which give rise to the reproductive power of their seeds (in 
which no trace of a cotyledonary embryo can be detected), and to inquire into the manner 
of the fertilization of their ovules. In the ordinary embryo, as is well known, its radicle, 
under conditions favourable to its development, extends into a root, while the rising 
stem and its first leaves are produced by the expansion of the plumule and cotyle- 
dons; in that exceptional condition of the embryo, such as in Cuscuta, Orobanche, 
Arum, &e., where the cotyledons, plumule, and radicle are fused into a fleshy mass, 
there is always some pullulating point on its surface out of which the young stem and 
its root are expanded. But no development of such a nature has been found in any of 
the Rhizogens: indeed all our knowledge on the subject of their reproduction is purely 
negative; that is to say, although nothing absolutely certain is yet ascertained on this 
point, we assuredly know that the mode of the germination of its seeds is different from 
that of all other classes, and that in this particular alone the Rhizogens stand quite 
isolated. On this topic many hypotheses have been suggested, none more probable than 
that of Mr. Brown, who suggested (Linn. Trans. xix. 232) the possibility that, in all 
these plants, their propagation is effected by the generation of cellular tissue proceeding 
from the sporuliferous contents which compose their peculiar kind of ** homogeneous 
embryo," the growing molecules of which penetrating and extending under the bark of 
the parent stock, by their progressive development, produce new and fully matured 
parasites, a development in its ultimate results as effective as the growth resulting from 
the cotyledonous embryo, which in Exogenous and Endogenous plants is considered 
essential to their reproduction. We have, however, as already stated, no positive evi 
dence by which this ingenious hypothesis can be supported. 
In regard to the fertilization of the ovule, although we are not aware of the manner 
in which this takes place, we are quite certain that an impregnation of some kind mus 
be effected in Rhizogens. In the Burmanniacee we find all the usual sexual paris # 
perfectly developed as in the higher orders of Endogens and Exogens—that is to 525: s 
perfect perianth, stamens completely formed, anthers charged with grains of pollen po% 
sessed of the same mode of expansion and apparent function ; for, in some cases, we see 
the pollen-tubes issuing from each anther-cell and brought into contact with a 3-lobe 
stigma provided with papillose surfaces; from this point we trace the usual stigm® j 
channels through the style, and sometimes (but not always) thence through other 
passages, which convey the fecundating influence to three parietal placentæ in the wait 
