Chapter XX 



— 221 



Summary and Conclusions 



may, under some conditions, separate from the vacuolar liquid 

 (vacuolar contraction). 



The large vacuole of mature cells is capable, under certain influ- 

 ences, of losing its water and of fragmenting into minute, semi- 

 fluid, chondriosome-shaped elements. The various aspects of the 

 vacuolar system are, therefore, reversible and seem to depend upon 

 the water content of the cytoplasm. 

 Water may move into the cytoplasm and 

 out of the vacuoles and the reverse ac- 

 tion may take place. The vacuoles 

 themselves, during dehydration of the 

 seed, are capable of losing water to the 

 point of being transformed into solid 

 bodies (aleurone grains) which later, 

 at germination, again become vacuoles 

 after taking in water. 



Although in their semi-fluid state 

 the vacuoles may very much resemble 

 the chondriosomes and the plastids, 

 they are always distinguishable from 

 these elements by their histochemical 

 behavior, notably by their instantane- 

 ous staining with vital dyes, such as 

 neutral red and cresyl blue, which stain 

 neither the chondriosomes nor the plas- 

 tids. They are to be distinguished from 

 these elements also by the fact that the 

 staining is essentially vital and ceases 

 as soon as death of the cells occurs, 

 whereupon the protoplasm is stained. 

 This is very different from the sub- 

 lethal staining of the chondriome which 

 almost never occurs except in dying cells 

 and persists after the death of the cells. 

 Furthermore, the histochemical be- 

 havior of the vacuoles is very variable 



and even the chondriosome-shaped vacuoles differ essentially from 

 the chondriosomes, by the fact that the former have no defined 

 characteristics. In general, they do not stain either by mito- 

 chondrial techniques or by other methods of fixation but in all 

 well differentiated preparations they appear as colorless canaliculi. 

 In the case in which they are stained by mitochondrial techniques, 

 they then appear as small vacuoles in which the colloidal content 

 has been precipitated and stained. This does not permit them to 

 be confused with the chondriosomes. Aleurone grains, which are 

 dehydrated vacuoles, always stain with mitochondrial techniques 

 and without their contents being precipitated. In some lower 

 plants, fungi for example, the chondriosome-shaped vacuoles con- 

 tain a substance called metachromatin, capable of being precipi- 

 tated with alcohol, but which does not stain with mitochondrial 



Fig. 152. — Diagrammatic re- 

 presentation of the vacuolar sys- 

 tem in phanerogam cells vitally 

 stained with neutral red. 1, embry- 

 onic cell; small, semi-fluid, chon- 

 driosome-shaped vacuoles composed 

 of a very condensed colloidal sub- 

 stance, homogeneously and deeply 

 stained. 2, differentiating cell; 

 vacuoles enlarged by absorption of 

 water and united in a network. 

 3, later stage; small vacuoles 

 unite to form a few large, un- 

 stained, liquid vacuoles containing 

 a dilute colloidal solution; the dye 

 causes flocculation of the colloids 

 as deeply stained precipitates 

 showing Brownian movement. 4, 

 mature cell; fusion of vacuoles to 

 form a single large one v/ith 

 deeply stained precipitates. 



