52 THE TISSUES OP PLANTS. 



plied, — in young developing organs exists in the greatest 

 abundance, not only in the interior of their cells, but also 

 in their intercellular spaces. 



M. Mirbel, to whom vegetable anatomy owes so many 

 beautiful discoveries, believes that the cytoblasts form in 

 the midst of the fluid which fills these intercellular spaces. 

 He gives the following account of their formation. In the 

 points where the new cells are beginning to form, we see 

 appear small gelatinous globules. This is the commence- 

 ment of the organization of the fluid. Very soon, each of 

 these globules, at first perfectly transparent, shows a little 

 spot slightly opaque ; this results from the formation of 

 a cavity in its interior, and we have a globular cell formed 

 which is the second degree of the transformation of the 

 nutritive fluid. This cavity dilates itself, the walls become 

 more and more transparent, and the tissue newly-formed 

 finally presents the same characters as the older cells with 

 which it thus becomes associated. 



This theory of Mirbel has been opposed by many phyto- 

 tomists, and especially in Germany by Unger and Mohl; 

 but it is probably true with reference to such tissues as are 

 swollen and succulent, and of a rapid growth, where the 

 cells remain loosely aggregated, and retain in any great 

 measure their spherical form. 



These intercellular spaces exist equally in the more 

 dense and compact tissues, where the cells become angular 

 and polyhedral by mutual pressure ; but they are very 

 much reduced in size, for the walls of the contiguous cel- 

 lules in this instance, touching almost completely by all 

 their points, must necessarily render these spaces almost 

 imperceptible. 



These views of Blirbel have been in some measure con- 

 firmed by the researches of Schleiden; and as his* ideas 



