PART SECOND. 



PHYSIOLOGICAL BOTANY. 



CHAPTEK I. 



OF THE VEGETABLE CELL. 



636. Revelations of the microscope. We have now completed a brief sur- 

 rey of the phenomena of visible vegetation. We commenced with the root and 

 now the consideration of the s"eed with its embryo completes the circle and brings 

 us around to the root again. We have studied hitherto superficially, as best we 

 were able by the unassisted eye. But the microscope opens to us a new world in 

 botany, more wonderful and fair, if possible, than that which we have already sur- 

 veyed. No just appreciation of microscopic botany can be obtained from drawings 

 or descriptions. Here the microscope itself is the only adequate teacher. 



637. Next inquiries. We have seen and studied the general organs of vegeta- 

 tion and their metamorphoses ; but of what aro these organs made ? What their 

 structure within t What their office and use in the life and growth of the plant ? 

 These inquiries must next bo answered. 



638. Structure op plants cellular. All forms of vegetable structure, how- 

 ever numerous and diverse, are alike composed of little bladders, called vescicles or 

 cells. We can often discern the cells in some structures with the naked eye, as in 

 the pith of elder, pulp of snowberry, and especially plain in the pulp of orange. 

 Other structures, which appear as a solid mas3 to the eye, aro seen at once, under 

 the lens, to consist of cells also — even the most solid wood or the stony substance 

 of the peach. A thin cutting (shaving) from the rhizome of the blood-root, magni- 

 fied 100 diameters, appears in outline (to say nothing of its brilliant coloring) as here 

 sketched (557). Thereforo 



639. The cell is the elementary organism which by its repetitions 

 makes up the mass of all vegetation. It is defined as a closed sac com- 

 posed of membrane containing a fiuid. 



640. The primary form of the cell is spheroidal. In some cases 

 it retains this form during its existence, but generally, in growing, it 

 takes new and various forms, which, on account of the two causes which 

 control them, may be classed as inherent and casual. 



641. The inherent forms of the cell, or those which depend 

 upon its own laws of growth, may be referred to three general types ; 



