54 MR. J. MIERS ON THE FAMILY OF TRIURIACE^E. 



small area of its surface, of several minute oblong cellular bodies, wbich soon enlarge, 

 others in great numbers being successively formed in their centre. These rudimentary 

 processes soon become more and more elongated, their growth being very rapid, until they 

 acquire five or six times the length of the original globular nucleus, from which, when 

 fully developed, they finally detach themselves, the nucleus remaining enveloped in the 

 swollen integuments. This new production thus assumes the form of a large plumula, 

 still more highly developed than that of Ceratophyllum, and separates in the manner above 

 described, as the germ of a future plant, consisting of an immense number of subulate 

 thread-like processes, at least an inch long, which are furnished with vessels, but their 

 chief bulk is cellular, the cells containing a number of green globules. Mr. Griffith re- 

 marks, that the cells of the nucleus, as well as of the processes, in an early stage of their 

 development, abound in active molecules, possessed of an exceedingly rapid oscillatory 

 motion; and it is obvious, from the universal presence of these corpuscles during the 

 formation of tissue, that they play an important part in this most obscure process. Mr. 

 Griffith considered the nucleus to be the cotyledon, the processes as forming a plumula, 

 and the neck, which united them at base and which is seated upon the globular cotyledon, 

 to be the radicle ; but these parts do not seem to bear any analogy to such elementary 

 portions of the ordinary embryo of phsenogamous plants, as is evinced by the quite unusual 

 position of what is here considered a radicle, between the cotyledon and plumula, and by 

 the fact of the detachment of such cotyledon, which has always been held to be necessary 

 to the completion of the germinating functions of the radicle and plumula. Mr. Griffith 

 endeavoured to explain these contradictions by ingenious reasonings, which, however, are 

 far from being satisfactory, as he was forced to acknowledge that this case forms a re- 

 markable exception to the general law of the absolute necessity of a cotyledon in a distinct 

 embryo, and that it is only to be accounted for on the plea that the presence of such a' 

 highly developed plumula obviates that necessity. These anomalies, however, appear to 

 me more satisfactorily explained by considering the original nucleus in the light of a 

 simple protoblast, from which a certain number of its cells, animated by the oscillatory 

 motion of the active molecules, as described by Mr. Griffith, pullulate and attain a rapid 

 increment, by the production of a number of thread-like cellular processes (or protophylla) 

 united at their base by the common centre of the original germinating cells (or epiblast). 

 The plumula of Griffith may thus be considered simply as an aggregated bundle of proto- 

 phyls, destined to form the germs of future leaves ; and his radicle may be viewed merely 

 as an epiblast, which, however, performs all the functions of a radicle, by subsequently 

 generating from its former point of attachment other cells to constitute future rooting 

 fibres ; and his cotyledon remains only the original protoblast, which having thus performed 

 its function of elaborating a gemmiferous prototype, becomes detached from its offspring. 

 Under this point of view the embryo of Cryptocoryne may be considered as protoblastous, 

 and not as cotyledonous, and the anomalies above shown vanish without calling in aid 

 forced exceptions to the ordinary laws of development. 



The Pistiece, considered as a suborder of the Aroidece, present some circumstances ana- 

 logous to the structure of Sciaphila. On examining the seed of Pistia obcordata, I find 

 that what has been described as its testa is in fact an arillus, which in some degree may 



