1915] CURRENT LITERATURE 329 
very accurate scientific methods to the problem of crop yield. The work, 
with its excellent analytical methods, deserves the careful attention of students 
of field crop production. When such methods are in general use in this phase 
of agronomy, the results and conclusions gained will carry with them much 
more weight and dependence. One is especially impressed with daily deter- 
minations of growth rate and flower and boll opening, which make possible the 
evaluation of accidental and temporary factors. Aside from the important 
contribution to method in analysis of agricultural yield, which after all is its 
greatest value, the article also contributes some clear-cut conclusions upon 
spacing as effecting production in the Nile valley, as follows: ‘‘( e 
ment shows that the yield of a cotton crop is primarily dependent on the 
number of flowers which it forms; (6) the normal extension of the root system 
of an isolated cotton plant can utilize more than 2 m.? of soil surface in soil 
which is more than 2 m. deep; (c) the plants in the field crop have only o. 18 m.? 
allowed them or less; most of the phenomena of field crop physiology in the 
fruiting seasons are traceable to the interference of one root system with 
ee (d) the’yield per unit area of the conventional spacing of the Egyp- 
nF ellah is the maximum obtainable under the limitations of field culti- 
Sth (two plants per hole, each hole 0.34 m. Wy (e) the sources of error in 
field experiments with cotton can be traced to (1) soil variation, especially 
stall pe a sasatant (2) wereqemerats ey = observation, whereb 
ethic ctua- 
tions of paste plants, eae of commercial varieties, ‘and normal 
physiological variations from day to day.”—WILLIAM Croc 
Geotropism of the grass node.—lIt is well known that lodged grass stems 
recover their vertical position by growth on the lower flank of the older mature 
nodes. Gravity, acting transversely on the stem rather than longitudinally, 
incites growth in these otherwise mature regions of the stem. ELFvING 
showed that these nodes are incited to growth when the stems are rotated 
with transverse exposure on the clinostat, thus giving a diffuse all-sided action 
of gravity; but in this case growth is equal on all flanks and no bending results. 
Riss has attempted to analyze more fully the mode of action of gravity in 
this behavior. She finds that when the gravity stimulus is applied inter- 
mittently but equally (intermittent clinostat) on two opposite flanks, the 
growth is greater than when it acts equally (continuous clinostat) on all flanks. 
By means of a compound centrifuge clinostat,4 she has applied a centrifugal 
stimulus of one gravity transversely (intermittently and continuously as 
above), at the same time the organ held its vertical position in relation to the 
pull of gravity. While the transverse stimulus thus applied incites growth, 
its effect is far less than in the absence of the longitudinal pull of gravity. 
3 Riss, M. M., Uber den Geotropism der Grasknoten. Zeitschr. Bot. 7:145~170. 
I9ts. 
4 See Bor. Gaz. “ 89. 1914. 
