ROOT HAIRS AND GROWTH 



371 



not only of comparing one ion with an- 

 other, one calcium compound with 

 another, and one more complete solution 

 with another, but also of comparing one 

 kind of plant with another. Mrs. Wanda 

 K. Farr has already begun this work. She 

 finds that rice, with respect to its root 

 hair elongation, exhibits a greater toler- 

 ance for acid and less tolerance for alkali 



Fig. 10. Calcium Nitrate Map 



POSED UPON THE CALCIUM CbXORID Map 



than do oats or collards. The acid limit 

 for rice was found to be pH z.5. 



ABNORMAL FORMS OF ROOT HAIRS 



The typical form for the root hairs of 

 many plants in air and in aqueous media 

 is cylindrical, straight, at right angles 

 to the root, with dome-shaped tip. The 

 root hairs of these same plants, however, 



growing in soil, take on many different 

 forms, as Sachs (67) described and figured 

 for wheat, oats, clover, and Selaginella. 

 This is doubtless a response to contact 

 with the soil particles, and to reactions 

 to the chemicals present in the soil solu- 

 tion. The hairs under these conditions 

 become enlarged at the tip, crooked, 

 knotty, and branched. The writer (iz) 

 has found that some plants, as buckwheat, 

 amaranth, millet, Saponaria, and Gyso- 

 phila, produce root hairs which are bent, 

 curved, or crinkled, even in aqueous 

 media. 



A number of investigators have accu- 

 mulated observations as to the effect of 

 external conditions in bringing about 

 changes in the form of otherwise typically 

 cylindrical hairs. Persecke was among 

 the first to describe the various forms of 

 root hairs. Schwarze noted a large 

 number of peculiar forms assumed by root 

 hairs of various plants in the presence of 

 soil particles, in various solutions, and 

 upon transfer to various liquid media. 

 Wortmann (88) observed some of these 

 forms of root hairs in sugar or potassium 

 nitrate solutions. Reinhardt (65) noted 

 the swelling of root hairs in these solutions 

 and the resumption of normal form later. 

 Sokolowa (76) has studied it very exten- 

 sively, attempting to correlate the changes 

 in form with nuclear position, lines of 

 flow of protoplasm, oxygen content of the 

 medium, etc. Stiehr (77) produced a 

 number of abnormal forms of root hairs 

 with organic compounds, such as sugars 

 and alcohols, and with the electric cur- 

 rent. Reference has already been made 

 to the observation of Jeffs (36) as to the 

 swelling of the hair in response to changes 

 in temperature. The writer has studied 

 the effect of calcium chloride and calcium 

 nitrate of different hydrogen ion and 

 molar concentrations upon the forms of 

 aquatic and amphibious root hairs. 



QUAE. BBV. BIOL., VOL. Ill, NO. 3 



