72 CARNEGIE INSTITUTION OF WASHINGTON. 



excessive length. Where the roots have been deprived of oxygen an 

 excessive length of time and are injured thereby, a delayed recovery 

 on the part of the shoot may be related to the necessity of forming new 

 roots upon the return to normal conditions of soil aeration. A few 

 selections can be made of typical experiments where the growth of the 

 shoot has been affected by inadequate root aeration. 



In the case of the cultivated sweet pea, culture No. 5 with this form, 

 shoot behavior was observed 3 days. The roots were in normal soil- 

 air the first and last days and in nitrogen continuously the second day. 

 In this experiment root-growth ceased in nitrogen and did not begin 

 again during the course of the experiment. The shoot grew as follows: 

 first day, roots in normal soil-air, 7 mm. ; second day, roots in nitrogen, 

 3.7 mm. ; third day, roots in normal soil-air, 8 mm. 



The results of work with the cultivated sunflower, on the other hand, 

 were not so consistent. Both root and shoot growth appeared to con- 

 tinue longer, however, than in the sweet pea or the garden bean. 



Shoots of Eriogonum sp., with the roots continuously in nitrogen for 

 8 days, had a daily growth-rate as follows: 8 mm., 11.3 mm., 8 mm., 

 13.3 mm., 15.5 mm., 11.7 mm., 13.5 mm., and 8.5 mm. In this instance 

 the temperature of the air as well as of the soil did not vary over 1° C. 

 in any day. 



The shoots of the potato hybrid, with the tubers still attached, ceased 

 growth very promptly upon the replacement of the ordinary soil-air 

 with nitrogen, or at least the growth-rate very markedly declined. For 

 example, in the experiment with culture No. 6 of this form, the shoot 

 increased 3.9 mm. in length in 41 hours, while the tuber and roots were 

 in normal soil-air, but during the subsequent 70 hours, when nitrogen 

 was used, the shoot-growth was only 2.3 mm., and this occurred mainly 

 at the commencement of the gas administration. 



In the morning-glory, Ipomoea sp., exposure of the roots for 48 hours 

 to nitrogen did not stop shoot-growth, although it slightly checked it. 



The shoot of tomato continued to grow, but at a decreasing rate, 

 for 4 days with root in nitrogen, and on the fifth day, when air was 

 again run in the culture, the growth-rate immediately increased. 



The roots of corn were exposed to nitrogen for 4 consecutive days, 

 and on the fifth day air was introduced. The daily growth amounts 

 of the shoot are as follows: 13.7 mm., 14.5 mm., 6.5 mm., 4.5 mm., 

 3.0 mm., and in air, 2.9 mm. In this case a renewal of a normal shoot- 

 growth rate would probably not be expected before fresh roots were 

 formed. 



The Dendrograph, by D. T. MacDougal. 



Two designs for a dendrograph which would obtain a continuous 

 record of growth and other changes in volume of tree-trunks during 

 an entire season were used in the construction of working models 

 which were used in preliminary tests on pines and oaks in 1918. 



