Chap, x The Problems of Growth 443 



clearly defined the condition of turgor, and showed the 

 intimate relation between this condition and growth. He 

 examined by careful measurements the gradual elongation 

 of a growing shoot, using for this purpose the auxanometer, 

 an instrument which he invented to record magnified 

 distances of the extension of a growing organ upon a 

 smoked paper surface. He showed also that two del mile 

 areas can be distinguished in an apical growing point, 

 the actual punctum vegetationis, in which cell division only 

 is occurring, and a region just behind it in which the 

 cells undergo increase in length. Sachs found that the 

 growing region, as distinguished from that of cell division, 

 is longer than it is in roots, several internodes taking 

 part in it simultaneously. Some years later, in 1880, 

 Askenasy showed that in some aquatic plants the region 

 of active growth may extend over as many as thirty to 

 fifty internodes. Sachs measured the growing zones in 

 roots as well as stems, and determined that the, second 

 zone is frequently nearly ten times as long as the first. 



The auxanometer was employed by Baranetzky in his 

 researches in 1879, and its form was much improved. 



Regions of intercalary growth were examined by Stebler 

 in 1878, and their distribution in many leaves determined. 

 He showed that in such regions a single zone of cell division 

 lies between two zones of active growth. 



The necessity of a supply of water as an antecedent 

 condition of growth was shown by Sorauer in 1873. He 

 found that the perfect development of the plant has a 

 distinct correlation with the condition of moisture in the 

 soil. De Vries also insisted on this relationship in 1877, 

 and confirmed Sachs by again drawing attention to the 

 necessity of regular and complete turgor of the cells as an 

 antecedent to growth, a condition which depends upon the 

 moisture of the soil. He showed that the position of 

 greatest turgor and greatest growth coincide. 



