242 VEGETABLE CELLS IN GENERAL. 



agents which cause it to contract by drawing-forth part of its 

 contents (Fig. 197). Its composition is indicated, by the effects of 

 re-agents, to be albuminous ; that is, it agrees with the formative 

 substance of the Animal tissues, not only in the proportions of 

 oxygen, hydrogen, carbon, and nitrogen which it contains, but also 

 in the nature of the compound formed by the union of these ele- 

 ments. The external layer, on the other hand, though commonly 

 regarded as the proper Cell-wall, is generated on the surface of the 

 primordial utricle after the latter has completely enclosed the 

 cavity and its contents, so that it takes no essential part in the 

 formation of the cell. It is usually thick and strong in comparison 

 with the other, and may often be shown to consist of several layers. 

 In its chemical nature it is altogether dissimilar to the primordial 

 utricle ; for it is essentially composed of Cellulose, a substance 

 containing no nitrogen, and nearly identical with starch. The 

 two constituents are readily distinguished by the action of Carmine 

 (§ 145), which stains the Protoplasmic substance, without affecting 

 the Cellulose-wall. The relative offices of these two membranes 

 are very different ; for whilst there are many indications that the 

 Primordial Utricle continues to participate actively in the vital 

 operations of the cell, it seems certain that the Cellulose-wall takes 

 no concern in them, but is only their product, its function being 

 simply protective. The contents of the Vegetable cell, being 

 usually more or less deeply coloured, have received the collective 

 designation of Endochrome (or internal colouring-substance) ; and 

 they essentially consist of a layer of colourless Protoplasm (or 

 organizable fluid, containing albuminous matter in combination 

 with dextrine or starch-gum) in immediate contact with the pri- 

 mordial utricle, within which is the more watery Cell-sap, particles 

 of Chlorophyll or colouring- substance and of Oil being diffused 

 through both, or through the former only. 



183. But although these component parts may be made-out 

 without any difficulty in a large proportion of Vegetable- Cells, yet 

 they cannot be distinguished in some of those humble organisms 

 which are nearest to the border-ground between the two kingdoms. 

 For in them we find the Cell -wall very imperfectly differentiated 

 from the Cell-contents ; the former not having by any means 

 the firmness of a perfect membrane, and the latter not possessing 

 the liquidity which elsewhere characterizes them. And in some 

 instances the Cell appears to be represented only by a mass of 

 Endochrome, so viscid as to retain its external form without any 

 limitary membrane, though the superficial layer seems to have a 

 firmer consistence than the interior substance ; and this may or 

 may not be surrounded by a gelatinous-looking envelope, which is 

 equally far from possessing a membranous firmness, and yet is the 

 only representative of the Cellulose -wall. This viscid Endochrome 

 consists, as elsewhere, of a colourless Protoplasm, through which 

 colouring particles are diffused, sometimes uniformly, sometimes 



