52 MR. J. MIERS ON THE FAMILY OF TRIURIACEjE. 



seen in Sciaphila, Hyalisma, and Soridium, and the figures he gives of it * quite corre- 

 spond with the details now offered of the seminal nucleus in these genera. Prof. Lindley 

 has long contended that these two families belong to a distinct class, which he calls Rhi- 

 zcmths or RUzogens ; but Mr. Griffith, in his able memoir above-quoted, wholly accords 

 with Mr. Brown's views on this subject, and states that these plants, though with inem- 

 bryonal seeds, or with what he calls a homogeneous-embryo-form structure, may, without 

 violating the rules of classification, be considered as aberrant forms of an imperfectly 

 developed state of exogenous or endogenous organization. Thus, Mr. Brown has always 

 considered the Rafflesiacece to be allied to the Aristolochiece, and Mr. Griffith contends 

 that the Ralcmophorece should be placed near the JJrticece. 



The considerations before stated naturally lead to the inquiry, if in such plants no em- 

 bryo exist, using that term in its ordinary signification, how is their propagation effected 

 by a seed with a simple nucleus of aggregated cells ? According to the views of most 

 modern physiologists, the earliest development of an embryo within the ovule is the forma- 

 tion of a germinal vesicle (primordial utricle of Mirbel), generated by the action of the 

 pollen-tube upon the embryonal sac, and the degree of perfection in the organization of 

 the cotyledon, radicle, and plumula, is evidently proportioned to the function requisite to 

 the future elaboration of the leaves, or a more or less complex stem ; but in the case of 

 leafless plants, the same amount of development would be useless for so simple an economy 

 of structure. This is even seen in plants of a very high degree of floral development, as 

 in Cuscuta, for instance, where the embryo of its seeds is altogether deficient (apparently) 

 of the usual requisites of cotyledons, radicle, and plumule f, as it consists of a simple 

 spiral thread, not germinating in the usual manner from two fixed points, but from which 

 pullulating vesicles are produced, indifferently from any point of its surface, thus proving 

 that the organization of the embryo bears an evident relation to the economy of the future 

 plant. The Orobanchece also present a very small undivided embryo, and the Monotro- 

 pece have a minute nucleus, in which neither cotyledon nor radicle is perceptible ; and this 

 is included in a reticulated arillus, as in Rurmcmniacece. Another instance, still more 

 striking, occurs in Cactece, where in the leaf-bearing genera the cotyledons are fully deve- 

 loped in the embryo, while in the leafless species the embryo is sobd and undivided. In 

 the same manner it is probable that in the Rurmcmniacece, Ralcmophorece, Triuriacece, &c, 

 the inembryonal nuclei, consisting of a series of germinating cells or cytoblasts, pullulate 

 at certain points, and thus perform all the requisite purposes of reproducing their very 

 simple forms of structure, in a somewhat analogous way to that in which the ordinary 

 embryo effects the more complex organization of vascular fibres and elaborate tissues in 

 the higher orders of Phsenogamous plants. 



If we admit the existence of an organ, thus endowed with the function, but wanting 

 the usual structure of the embryo, it should hold some adequate designation, and for this 

 the term Protoblastus does not seem inappropriate, as it effects the same purpose as the 

 gemmule or plumula J. The word used by Mr. Griffith for this organ, "homogeneous 

 embryo," would require that the ordinary embryo, in contradistinction, be called hetero- 



* Trans. Linn. Soc. vol. xx. pi. 8. fig. 9-14. f Lindley, Introd. to Bot. p. 217. 



J In a similar sense, Richard has applied the term llastus to the plumula of the seed in Gramineee. 



