36 THE AMERICAN MONTHLY [February, 



desmids are one-celled plants of die lowest type, we have here the vege- 

 table kingdom as it were in a nutshell, reduced to the last analysis. 

 The life-history of the individual cell forming, according to Schleiden,* 

 the true basis of the study of vegetable life in general, the desmids af- 

 ford admirable examples for just such study and furnish the key to the 

 whole problem. 



In the typical plant cell we have the cell-wall and the cell contents. 

 Now, this cell-wall is double, and the two layers are different ; the inner 

 is the more important of the two and it is practically identical with the 

 protoplasm which fills it, being albuminous in character and having 

 little to distinguish it but its thicker consistence and the absence of 

 granules. But the outer layer is made up of cellulose which, says Car- 

 penter, seems to be excreted from the surface of the inner layer. Now, 

 the sarcode of animals and the protoplasm of plants are identical. f We 

 may say then that the animal cell is free protoplasm, the plaitt cell 

 protoplasm enclosed and limited by a cellulose layer or covering. For 

 chlorophyll is not a necesssity to the vegetable cell ; it is absent in the 

 fungi and in lichens ; so close is the vegetable to the animal kingdom 

 at this point. Indeed, as Carpenter says, ' it is impossible to draw a 

 definite line of division between fungi and protozoa in some cases.' 

 The plant protoplasm excretes cellulose, the animal sarcode or proto- 

 plasm excretes chitin, and as the outer layer (of cellulose) is not essen- 

 tial} to the existence of the plant, nor the shell or test to the rhizopod, 

 we may say that the plant and the animal are identical so far as sub- 

 stance is concerned. Protoplasm and the primordial utricle — whether 

 ectosarc or ectoplasm — these are what really constitute protophytes and 

 protozoa alike. We may represent it by a circle of which the inner 

 portion is protoplasm and the boundary primordial utricle. Here are 

 the essentials of plant and animal, and they are the same in both cases. 

 The protoplasm is the same in each, the primordial utricle is the 

 same in each, nitrogenous, albuminous in plant as well as in animal. 

 A marvellous fact this and well worth remembering carefully. Add on 

 now a cellulose wall (represented by an outer boundary line to the cir- 

 cle) and you have the typical plant cell with its protoplasm limited by 

 the primordial utricle and enclosed in a layer of cellulose ; and the test 

 is carmine, which stains dead protoplasm but leaves the cellulose un- 

 stained. 



Under the contents of the plant cell we have chiefly to consider the 

 nucleus and the chlorophyll corpuscles. Note, again, that the former 

 is albuminous in both plant and animal, another striking bond of union, 

 as it is the very centre of vital activity. The initial force, therefore, 

 is of the same character in both kingdoms. Within the nucleus there 

 are frequently smaller bodies, the nucleoli. Others go still further and 

 speak of nucleo-nucleoli, and a recent writer, Conn, tells us that we 

 must, on this account, as well as for other reasons, entirely change our 

 ideas regarding the typical cell. But it is hardly necessary to do more 

 here and now than refer you to his striking article in the August num- 

 ber of the Microscopical Journal (1888), and to Prof. Whitman's ab- 

 stract in the same Journal for November. The chlorophyll corpuscles 



* Carpenter, The Microscope. 



t Max Schultze, quoted by Carpenter. 



t Encyclopaedia Britannica, Article on Biology. 



