PLANT-CELLS AND THEIR CONTENTS. 



291 



stem, roots, and branches of higher plants, some are tiniest rolling 

 spheres ; some stretch away to the length of several feet, and some 

 are microscopic specks. In Fig. 2 we have the representation of a 

 beautiful marine alga, unicellular, and yet thirty inches or more in 

 length. 



As we ascend the scale of life we find the individual cell more sub- 

 ordinate to the organism as a whole, and so less complex in itself ; and 



I .' Tllv ' ' T/','l 



F13. 2. Unicellular Alga (copied from Thom6.) 



yet, when we examine the cells which make up the tissues of the best 

 plants we can find, the blooming occupants of our hot-houses, gardens, 

 and fields, we meet with marvelous diversity, and are soon made to 

 feel that variety of form is the law, uniformity the exception. Fig. 3 

 represents the appearance of a cross-section of a stem of Tradescantia. 

 From this section we may learn not the variety of cell-forms only, but 

 something of the manner in which every plant is developed, and some- 

 thing of the porousness of all cellular structure. 



But let us tear off with our forceps a little shred of the epidermis 

 of some leaf. The leaf from a petunia will do ; that of the wild 

 Jacob's-ladder is better, and that of the wake-robin better still. Let 



