44 



BOTANY 



dark on a piece of filter paper, unequally moistened, the protoplasm 

 will become aggregated at the moister spots. The plasniodiuin also 

 has the peculiarity of growing against a slow stream of water, and 

 by allowing a stream to flow down a glass slide, by means of a strip 

 of filter paper dipping into a vessel of water, the plasniodiuin will 

 creep up the vertical slide, against the descending stream, and spread 

 itself over the wet surface. 



Adaptation. The extraordinary ability shown by certain organ- 

 isms to adapt themselves to changing conditions resides primarily, 

 of course, in the protoplasm, and this adaptability to environment 

 must be considered one of the manifestations of protoplasmic 

 irritability. 



Reproduction 



The living protoplast, by division into equal parts, or fission, shows 

 the simplest form of reproduction. This power is also shown by 

 the various essential organs of the protoplast, the nucleus and 

 plastids, and presumably is shared by the invisible pangens, or 

 ultimate protoplasmic units. 



THE TYPICAL PLANT-CELL 



With few exceptions, such as the ova and spermatozoids, the 

 protoplast of the vegetable cell is con- 

 tained within a definite membrane, the 

 cell-wall, usually composed of cellulose. 

 It was the cell-wall which first attracted 

 the attention of the early students of 

 vegetable tissues, who quite overlooked 

 the much more important protoplast. 



Until a comparatively recent time it 

 was assumed that the protoplast of the 

 simpler plants consisted of quite homo- 

 geneous protoplasm, but it is exceedingly 

 doubtful if such simple forms really 

 exist. The excessively minute size of 

 some cells, like certain Bacteria, may 

 account for the failure to demonstrate a 

 definite organization of the protoplast. 

 A further discussion of the structure of 

 the protoplast in the Bacteria and the 

 allied Schizophyceae will be deferred 

 until another chapter. 



In the cells of all typical plants there 

 may always be detected a nucleus (or 

 sometimes many nuclei) and usually one 



FIG. 29. Cell from a stamen- 

 hair of Tradescantia ; w, cell- 

 wall; pr, cytoplasm; n, 

 nucleus ; nu, nucleolus ; v, 

 vacuoles. 



