THE 



POPULAR SCIENCE 

 MONTHLY. 



JULY, 1882. 



PLANT-CELLS AND THEIE CONTENTS * 



By T. H. McBETDE. 



PROFESSOR OF BOTANY, STATE UNIVERSITY OF IOWA. 



A CHILD'S toy-balloon may afford us an illustration of what a 

 naturalist might call a typical cell. We have in the toy simply 

 a closed sac thoroughly distended by its contents, more or less per- 

 fectly spherical in shape, and affording in outline or cross-section an 

 almost perfect circle. In the organic cell the sac is known as the 

 cell-wall, and whatever may be inclosed by the cell-wall is called the 

 cell-contents. A typical cell would be round, spherical, but very few 

 cells, as they occur in nature, are perfect spheres. A cell which may 

 be spherical at the outset may change its shape in accordance with 

 changing circumstances, so that we may say that the form of all cells 

 which we find united to form tissues varies with the situation which 

 such cells occupy, and the functions of the tissues themselves. This 

 we shall see more clearly as we go on. That vegetable tissues, as they 

 occur in wood, pith, leaves, flowers, and fruit, are entirely composed 

 of cells, may be easily demonstrated. All that is needed is, to take a 

 very thin slice of any of these substances and examine with a micro- 

 scope of moderate power, when the cellular structure becomes imme- 

 diately apparent. So, then, all the great variety of form and color, and 

 all the resulting beauty, which the vegetable kingdom affords, and all 

 the varied economic value of plants, depends upon the form and con- 

 tents of these little organic units of cells. More than this : these cells 

 are of the highest scientific interest. All the discussion of the past 

 few years in regard to spontaneous generation and the origin of life 

 has been a discussion of vegetable cells ; and very much of all that we 

 know about life, its activity and its mystery, has been derived from 



* Illustrations from drawings by C. H. Dayton, Mary McBride, and the author. 



VOL. XXI. 19 



