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THE QUARTERLY REVIEW OF BIOLOGY 



of Hydrocharis rather intensively, using a 

 wide variety of intravital stains. He 

 used protoplasmic streaming as an index of 

 the normal condition of the cell. He has 

 been able to compare the effect of different 

 dyes on the cell and found that most of 

 them, with the exception of Chrysoidin, 

 cause alterations, which he regards as 

 injurious or lethal. He also found that 

 the cytoplasm is basic when alive and acid 

 when dead. Upon staining crystals ap- 

 pear in the hair. Whether these are pre- 

 cipitations due to the effect of the stain 

 upon otherwise soluble substances, or 

 whether they are simply making apparent 

 otherwise invisible solids, is not clear. 

 Martin has determined the hydrogen ion 

 concentration of root hairs of the sun- 

 flower to be from pH 4.4 to 4.0, which is 

 as acid as any cells of the plant and more 

 acid than many of them. 



In studying the root hairs of Lefidium, 

 Zacharias (89) detected the presence of 

 certain small bright bodies. They were 

 found to be in Brownian movement, which 

 was accelerated with transfer to solutions. 

 In certain hairs no glistening bodies were 

 present, and these hairs behaved differently 

 to chemical tests and in their reaction to 

 certain solutions. The writer (11) has 

 observed the appearance of glistening 

 bodies in hairs of collards, but only when 

 growing in very alkaline solutions. 



The osmotic pressure of the root hairs of 

 ordinary plants has been measured by the 

 plasmolytic method, that is, by deter- 

 mining the strongest solution which will 

 not cause shrinkage of the protoplasm. 

 Miss Roberts found that root hairs of dif- 

 ferent species were plasmolyzed by sucrase 

 from o.zz M to 0.4 M concentrations 

 after growing in air, and that in solutions 

 they maintain an osmotic pressure 4 to 6 

 atmospheres higher than the medium. 

 Ursprung and Blum (81) found an osmotic 

 pressure of 1.1 atmospheres, the lowest 



that they observed in any of the cells of the 

 plant. Miss Addoms (z), however, finds 

 that the root hairs are not plasmolyzed as 

 readily by either salts or sugars as are 

 other cells of the root, especially the root 

 cap and the cortex. She finds, for instance, 

 that 0.8 M sodium chloride or 0.5 M. 

 cane sugar will affect the latter tissues, 

 but not the root hairs. Popesco (64)- 

 obtained similar results with plasmolysis | 

 and argued, therefore, that root hairs 

 are not absorbing organs, whereas it 

 simply shows that they have a higher 

 osmotic pressure and therefore are more 

 efficient organs for absorbing water. 

 Ohga (58) found that the osmotic pressure 

 of root hairs is affected by the age of the 

 seedling and the medium. Bean, wheat, 

 and buckwheat root hairs were plasmo- 

 lyzed by 0.Z4 molar sucrase when the root 

 was 5-8 cms. long and had been growing I 

 in air, but 14 days later 0.36 to 0.54 M 

 concentration was required to plasmolyze 

 the hairs then growing in water cultures. 

 Ursprung and Blum (81) found that the 

 osmotic pressure of the root hairs depends 

 to some extent upon the medium in which 

 they are growing. It is 1.1 atmospheres 

 in saturated air. Upon transfer to pure 

 water it drops to 0.3 atmospheres in 

 eight days. Upon transfer to o.z M 

 sucrose it rises to 5.3 atmospheres in one 

 day. The plant thus has the ability to 

 adjust the osmotic pressure of root hairs 

 to approximate that of the surrounding 

 medium. It should be pointed out, how- 

 ever, that this adjustment is made, not by 

 changing the osmotic pressure of a given 

 root hair, but by sending out new root 

 hairs in the new concentration, having a 

 different osmotic pressure. Halophytes, 

 that is, plants which grow in soil high in 

 salt content, such as seaside plants, have 

 a much higher osmotic pressure in their 

 root hairs. Hill (34) found that Salicomia, 

 for instance, will not be plasmolyzed by 



