the Nitrogenous Matter of Plants. 35 



irregular spheres; whilst in the cells of young specimens of Cham, 

 of Hydrocharis morsus-rance, of Stratiotes aldides, Caulinia fragilis, 

 and Sagittaria sagittifolia, in the hairs of young shoots of Borago 

 officinalis, in the epidermis of the petioles of young specimens of 

 Arum, &c, it is represented only by some viscous flakes having 

 no determinate figure. The nucleus, therefore, being essentially 

 a variable organ, has not failed to give birth to the most divergent 

 opinions relative to its nature, origin, and functions; and we 

 should not materially err in asserting that there are not two 

 botanists who entirely concur in respect to its composition or to 

 the part it is intended to play in the economy of the cell. Yet, 

 though this body is susceptible of assuming different aspects, the 

 one under which it usually presents itself is that of a spheroid, 

 in the form of a globule of mucus, having at its centre a collec- 

 tion of semi-transparent granules endowed with sufficient soft- 

 ness to make them adhere feebly together. Now, the presence 

 of this granular matter in the centre is suggestive of the existence 

 of a membranous pellicle about the periphery or surface; and 

 some researches which I have made on this point prove to my 

 mind that this supposition is well founded. Thus, to demon- 

 strate the fact in the epidermis of Tradescantia virginica, it is only 

 necessary to treat the slice of tissue under observation with a 

 drop of liquid ammonia, which causes the disappearance of the 

 internal collection of granules, and renders visible a membranous 

 disk, which is no other than the collapsed sac within which the 

 granules were contained. However, this soft pellicle is so very 

 transparent, and of such tenuity, that it is oftentimes very diffi- 

 cult to distinguish its outline with clearness, particularly if, as 

 very often happens, it lies in contact with the wall of the 

 cell. 



If, in place of employing the epidermis (which, by the way, 

 need always be very transparent), choice be made of parts richer 

 in water, such as the young root-fibres, the spongioles, the stem 

 of young fleshy plants, the petals, &c, the study of this organ is 

 facilitated ; for, under these circumstances, the granular heap is 

 less abundant, and the little membraniform hyaline sac which 

 envelopes it is more perceptible, whilst at the same time the pre- 

 sence of liquid within the sac, apparently of rather stronger re- 

 fracting-power than the fluid in the cell-cavity, may be detected 

 on submitting the preparation to the action of a dilute acid or of 

 alcohol of 86° ; the little sac may be seen to contract and shrivel, 

 to force out a portion of the liquid it contains, and to become 

 reduced to one-third or one-fourth of its original dimensions. If 

 the preparation be now moistened with a little liquid ammonia 

 of 12°, the small sac regains its primitive form, though at the 

 same time it acquires a somewhat larger volume than before, 



3* 



