GENERAL CHARACTERISTICS 75I 



TABLE 1 

 COMPOSITION OF PUTATIVE^ CELL-WALLS OF SEEDLINGS 



All data are percent of the dry weight 



1 Material remaining after grinding and thorough extraction first with cold and then with 

 hot water considered as cell-wall. 



2 Data only supplied for cell-wall plus water-soluble (cytoplasm). 



^ This figure includes such small amounts of lignin as may be present in the etiolated material. 

 ■* The proportion of true polyuronides is probably lower than that given for pectic 

 substances; in the case of oat coleoptiles not more than one half. 



cytoplasm by the fine threads which are in constant streaming motion. In most 

 large-vacuoled cells of land-plants, however, the nucleus is against the wall in the 

 peripheral cytoplasm, which circulates around the whole vacuole ("cyclosis"). 

 The cambium cells of many trees change their vacuolar type from the multiple- 

 globule type in the fall and winter through rather unstable types containing 

 changeable thread-like or "myelin" forms to the large central vacuole in the 

 growing season (Bailey, 1930; Fig. i). 



The liquid or "sap"' in the large vacuoles usually is a relatively dilute solution, 

 though highly concentrated tannin-containing vacuoles are known. It often con- 

 tains red or yellow pigments, the anthocyanins and anthoxanthins, in solution, 

 and commonly it contains acidic and aromatic materials which stain intensely 

 with Neutral Red. If the vacuole is acid it may even give a flocculent deeply 

 colored precipitate with Neutral Red. Since it is relatively dilute and fills up so 

 large a fraction of the cell volume, it follows that the increase in volume during 

 growth is largely due to the intake of water into the vacuole. This consideration 

 has dominated much of the work on plant growth. 



II. DEFINITIONS 



Before going further it will be convenient to define and discuss terms which will 

 be used throughout this chapter. 



Growth will be used in the sense of enlargement, either of a cell, a tissue, an 



Literature p. 8i6 



