THE INITIATION OF THE REPRODUCTIVE PROCESSES 185 



hydrates and nitrates. Hence, in the absence of any other Hmiting 

 factors for vegetative development, the balance of carbohydrate manu- 

 facture over utilization depends on the nitrate supply. When this is 

 kept high, though carbohydrates are manufactured in large quantities, 

 they are immediately utilized for vegetative development and the plants 

 are unfruitful and vigorously vegetative. If the nitrate supply is reduced 

 moderately, carbohydrate utilization is checked and there is opportunity 

 for carbohydrate accumulation; fruitfulness follows. To be sure carbo- 

 hydrate accumulation occurs when the nitrate supply is still further 

 reduced, but here the situation is comphcated because nitrate then 

 becomes a limiting factor to fruitfulness by inhibiting such vegetative 

 development as appears necessary for fruit bud differentiation. Plants 

 of this type are stunted and altogether lacking in nitrate nitrogen. 



Influence of the Moisture Supply. — Nitrate supply is not the only factor 

 which may determine the balance of carbohydrate manufacture over 

 utilization. This may be accomplished also by a decrease in any other 

 factor involved in the process of growth and development. For example, 

 Kraus and Kraybill report that "withholding moisture from plants grown 

 under conditions of relative abundance of available nitrogen results in 

 much the same condition of fruitfulness and carbohydrate storage as 

 the limiting of the supply of available nitrogen." A diminution of the 

 water supply is well known to be frequently associated with fruitfulness. 

 In this case, as in that of nitrate supply, there is probably a limit beyond 

 which a further reduction of the water supply results in unfruitfulness 

 and stunted growth. 



Influence of Other Factors. — Klebs^^^ concluded from numerous investi- 

 gations that a reduction in the supply of nutritive salts leads to the fruit- 

 ful condition provided there be adequate facilities for photosynthesis 

 and hence for carbohydrate accumulation. Recent work of Walster^^^ 

 has shown that heat may be a limiting factor to vegetative development 

 as well as water or any of the essential nutrient and food materials and 

 that diminished heat, even with a high nitrogen supply, leads to carbohy- 

 drate accumulation and culm formation in barley. These investigations 

 indicate that any environmental factor may check growth and lead to 

 carbohydrate accumulation and that fruitfulness may result provided 

 vegetative development is not seriously retarded or altogether stopped. 

 It is shown later in this section that vigorous vegetative growth is not 

 inimical to fruitfulness. On the contrary, the facts just presented indi- 

 cate that fruitfulness and vegetative development are associated functions. 



FRUIT-BUD FORMATION 



Since carbohydrate accumulation seems associated with fruit bud 

 differentiation and the conditions for carbohydrate accumulation change 

 during the season, it is evident that there must be considerable variation 



