480 
AMERICAN JOURNAL OF BOTANY 
[Vol. 10, 
and the third through embryo abortion. As to just how far genetic factors 
enter in the failure of so many normal-appearing pollen grains to germinate 
or of apparently normal seeds to grow, it is difficult to state because so 
many other considerations also enter. 
Nutritional Considerations. The research on the relation between 
nutrition and sterility, or the broader question of fruit-setting, while not 
easy to summarize, points to a solution of many phases of the problem. 
The results include and overlap some things which have heretofore been 
given other interpretations, and have progressed from a study of the effect 
of nutrition on the plant as a whole to a study of the effect on the fruiting 
unit, such as the branch, spur, node, or even the individual flower. Nutri¬ 
tional studies are complicated by the variations encountered in seasons, 
soils, moisture supply, and in the nutritional requirements of the several 
horticultural crops. 
Some things, however, appear to be well established. The importance 
of size of plant or tree in relation to yield is becoming recognized, especially 
in the tree fruits. The primary factors in obtaining size appear to be 
nitrogen and soil moisture. The whole orchard program should be directed 
toward a control of these two factors as they bear upon the extension of 
the fruiting area, fruit-bud initiation and formation, fruit-setting, fruit 
maturity, dormancy, and hardiness. The early period of rapid growth, of 
the tree fruits particularly, should be kept in mind, because fruit-bud 
initiation and formation accompany the period of vegetative extension. 
While many of the details have not as yet been worked out, it appears that 
the most favorable conditions for growth, fruit-bud initiation and develop¬ 
ment, and fruit-setting and maturity may be somewhat conflicting. The 
conception of the carbohydrate-nitrogen balance (Kraus and Kraybill, 
1918) furnishes a workable basis for cultural practices, and the control of 
fruitfulness depends primarily upon proper pruning, the application of 
nitrogen, and the conservation of moisture. 
While skilled growers have for some time recognized the unfruitfulness of 
exceptionally vigorous as well as of exceptionally slow-growing plants, the 
variation in the response of the different fruits complicates the control of 
fruitfulness. For instance, in the apple young trees, or old trees heavily 
pruned, are generally found to be unfruitful, and some varieties may be 
fruitful when interplan ted with others which are unfruitful. In fact, York 
Imperial is sometimes so near the border line between the fruitful and non¬ 
fruitful conditions that some limbs on a tree bear fruit while others on the 
same tree do not. In the peach, on the other hand, yield is closely correlated 
with vigor (Alderman, 1915). Likewise, the red raspberry responds very 
readily to nitrogen (Chandler, 1920) and is seldom oversupplied with it, 
while the black raspberry and blackberry make less response. In general, 
however, these differences are limited, and up to a certain point in all 
species, size of fruit and yield accompany strong growth. 
