THE CELL-THEORY 257 



2. In 1837-8, each utricle of the plant was considered to have the 

 following composition. In the first place, there was the cellulose cell- 

 wall, or the portion of periplast answering to any particular endoplast ; 

 secondly, there were the cell-contents, a substance of not very defined 

 nature, which occupied the cavity of the cell ; and thirdly, there was 

 the nucleus, a body to whose occurrence attention was first drawn, as is 

 well known, by our own illustrious botanist, Robert Brown. He, 

 however, cautiously remarked only its very general occurrence, without 

 pretending to draw any inference from the fact ; while Schleiden made 

 the belief in its existence, in all young tissues, the first article of the 

 faith botanical. This is, however, most certainly incorrect ; there is no 

 trace of a nucleus in many Algae, such as Hydrodictyon, Vaucheria,i 

 Caulerpa ; in the leaf of Sphagnum, nor in young germinating 

 Ferns. ^ 



Whatever opinion may be entertained upon this head, there is one 

 point quite certain — the enumeration of the elements of the vegetable- 

 cell given above is incomplete ; there being one, and that the most 

 important, which is omitted. We refe r to ^h& primordial utricle, which 

 w as only disco vered by Von Mohl in 18^. This" is a nitrogenous 

 me mbrane, wh ich always lies \x^ close contact with the periplast, and 

 forms, in fact, an JncLudfid-vesicJer- within whicb the 'Lcontents"- and 

 the nucleus lie. Instead, therefore, of the endoplast consisting merely 

 orcontentsaHd a nucleus, it is a vesicle containing the two latter, when 

 they exist at all ; and they are of subordinate importance, for while, 

 as we have seen, a nucleus and formed contents may be absent in 

 young or even fully formed tissues, the primordial utricle is invariably 

 present in the young structures, and often persists until they have 

 attained their full size. Since, then, the functions of the vegetable 

 " cell " can be effectually carried on by the primordial utricle alone ; 

 since the " nucleus " has precisely the same chemical composition as 

 the primordial utricle ; and since, in some cases of cell-division, new 

 nuclei are seen to arise in the substance of the endoplast, by a mere 

 process of chemical and morphological differentiation (Von Mohl, 1. c, 

 p. 52), it follows, we think, that the primordial utricle must be regarded 

 as the essential part of the endoplast — the protoplasm and nucleus 

 being simply its subordinate, and, we had almost said, accidental 

 anatomical modifications. 



3. Finally, with respect to Schleiden's observations upon the mode 

 of cell-development, according to which in all cases the new production 

 of vegetable-cells takes place by the development of nuclei, round 



1 On Alex. Braun's authority, Ueber Verjiingung, &c., p. 1S6. 

 ^ Henfrey, Linn. Trans. 1853. 



S 



