MICROSCOPICAL RESEARCHES, 



&c. &c. 



INTRODUCTION. 



Although plants present so great a variety of external form, 

 yet they are no less remarkable for the simplicity of their 

 internal structure. This extraordinary diversity in figure is 

 produced solely by different modes of junction of simple ele- 

 : mentary structures, which, though they present various modi- 

 fications, are yet throughout essentially the same, namely, cells. 

 The entire class of the Cellular plants consists only of cells ; 

 many of them are formed solely of homogeneous cells strung 

 together, some of even a single cell. In like manner, the Vas- 

 cular plants, in their earliest condition, consist merely of simple 

 cells ; and the pollen-granule, which, according to Schleiden's 

 discovery, is the basis of the new plant, is in its essential parts 

 only a cell. In perfectly- developed vascular plants the struc- 

 ture is more complex, so that not long since, their elementary 

 tissues were distinguished as cellular and fibrous tissue, and 

 vessels or spiral-tubes. Researches on the structure, and par- 

 ticularly on the development of these tissues, have, however, 

 shown that these fibres and spiral-tubes are but elongated cells, 

 and the spiral-fibres only spiral-shaped depositions upon the 

 internal surface of the cells. Thus the vascular plants consist 

 likewise of cells, some of which only have advanced to a higher 

 degree of development. The lactiferous vessels are the only 

 structure not as yet reduced to cells ; but further observations 

 are required with respect to their development. According to 

 Unger (Aphorismen zur Anatomie und Physiol, der Pflanzen, 



D. H. HILL LIBRARY 1 



North Carolina State College 



