Paet I. 

 THE CELL. 



I. INTEODUCTION. 



The organisms which we designate as plants, though variable, 

 have one thing in common : they are either single cells or cell- 

 complexes. There is, so to speak, only one element in plants, and 

 that is the cSl. Every plant consists of at least one cell. 



Omitting for the present the embryonic conditions of the cell, it 

 may be defined as, for the most part, a microscopic dosed vesicle 

 consisting of wall or covering and contents (large cells, as those of 

 Gossypitmi species, 6 cm. long ; medium-sized cells, as those of elder- 

 pith). We must distinguish between younger and older stages of 

 the cell. At first an apparently homogeneous, mucous, tenacious 

 substance — plasm^ protoplasjn — fills the entire cell-cavity {lumen) 

 and is enclosed by the cell-wall [memhrane). The components of the 

 cell-contents designated by the collective noun "plasm" are alhumi- 

 noid substances and hence contain besides carbon, hydrogen, oxygen^ 

 also nitrogen, sulphur, and sometimes phosphorus. Its mucous consist- 

 ency is noticeable by its spontaneous escape from openings of the cell- 

 wall (swarm-spore formation of algse, etc.). Gradually there appear 

 differentiations in the apparently homogeneous plasm. Spherical 

 particles filled with a watery substance — vacuoles ' — are distinguish- 

 able from the more dense contents ; the latter, the true plasm, are of 

 different kinds, not homogeneous, as a superficial examination would 

 indicate. The plasmic titricle, which is of special importance, shall 



• According to more recent investigations (Went) the " vacuoles" originate 

 from pre-existing ones. (The conclusions of this investigator are generally con- 

 ceded to be erroneous. — Trans.) 



4 



