S. DEPARTMENT OF AGRICULTURE. 
continued through a longer period during the da}' than on the other 
plats. Increasing the soil moisture in plat 1 was effective in pre- 
venting this wilting for only a short time. In six or seven days 
subsequent to an irrigation the plants would again show a loss of 
turgor of the leaves under the heat of the sun toward the middle of 
the day. 
Balls (J), in considering the functions of the cotton root system, 
states that "since deficient water absorption is the real limiting 
factor in the sunshine effect, it follows that the size of the root sys- 
tem is the true limiting factor of water absorption and that the 
humidity of the soil may vary between wide limits without affecting 
it." In the effort to determine whether there was any difference in 
the root systems of plants on the four plats which might account 
in part for a deficiency in water absorption by the larger plants, 
excavations were made on March 1, 1920, and several plants were 
removed from the ground with all of the roots that could be traced 
in the upper 18 inches of soil. It was found that the roots had 
lived through the winter, and only a few of those uncovered showed 
any signs of decay. A count was made of all lateral roots attached 
to the 18 inches of taproot, a summary of which is given in Table III. 
Table III. — Count of lateral roots attached to top 18 inches of the taproot of 
Pima cotton in 1919. 
Plat. 
'■ Mean n um- 
ber of 
laterals. 
Number 
of 
observa- 
tions. 
No. 1 
34.6±1.56 
13 
No. 2 
32.lil.49 
15 
No. 3 
-.. 24. 4+1. OS 
17 
No. 4.... 
- 
38. 2±1.09 
30 
, 
It is not a far-fetched supposition that the earlier irrigation re- 
ceived on June 10 by the plants on plats 1 and 2 would have encour- 
aged the production of lateral roots near the surface of the ground 
and that the roots of plants not receiving early irrigations would 
have been forced to make their way into the deeper subsoil in order 
to obtain moisture, while the formation of laterals in the dry topsoil 
would have been somewhat suppressed. It appears from the results 
shown above that this did not occur. While a considerably greater 
number of laterals was found on plants from plats 1 and 2 than 
on -those from plat 3, the greatest number of laterals was found on 
the plants removed from plat 4. It is not inconceivable that the 
liberal application of fertilizer supplied to plat 4 might have some 
bearing on the occurrence of this large number of surviving laterals 
in the topsoil, but until more detailed investigation has been com- 
