CARBOHYDRATES AND NITROGEN METABOLISM 453 



The effect of the relative availability of carbohydrate and organic nitrog- 

 enous compounds upon the reproductive phase of growth is a more complex 

 phenomenon than the influence of the proportionate quantities of those two 

 foodstuff's upon vegetative development. The reproductive process involves 

 a complex series of phenomena among the more important of which are the 

 initiation and maturation of essential floral parts, the development of mega- 

 spores and microspores, the formation of viable egg cells and pollen, pollina- 

 tion and growth of the pollen tube, fertilization, and finally development of 

 the embryo, seed, and fruit. Different stages in this process are variously 

 influenced by the carbohydrate and nitrogen metabolism of plants. 



In perennial species further complications arise from the fact that differ- 

 entiation of floral parts may occur during one growing season, but their 

 maturation does not take place until the next one. Certain phases of the 

 development of perennial species may be influenced as much by the carbo- 

 hydrate-nitrogen metabolism of the preceding season as by that of the current 

 year. 



In many annual species the number of flowers produced is conditioned 

 partly by the extent of the previously developed vegetative body of the plant. 

 Hence if metabolic conditions do not favor vegetative development during 

 the earlier stages of the growth cycle this may result in a decrease in the 

 number of flowers produced. 



Although flower primordia apparently will form on plants over a wide 

 range of metabolic conditions, in general occurrence of the complete cycle 

 of reproductive processes may be checked by a lack of either carbohydrate or 

 nitrogenous foods. A deficiency of carbohj-drates has been found to induce 

 microspore degeneration and pollen sterility in the tomato (Howlett, 1936) 

 and apparently has a similar effect in many other species. Nitrogen deficiency, 

 on the other hand, seems to have relatively little effect on anther development 

 and pollen fertility. The converse appears to be true of the female organs. 

 Their development is not greatly influenced by carbohydrate deficiency, but is 

 markedly repressed by nitrogen deficiency. In hemp (a dieocious species) the 

 male plants characteristically have a higher carbohydrate content than the 

 female plants, but the nitrogen content of the latter is higher (Talley, 1934)- 



The development of fruits is often physiologically the equivalent of the 

 initiation of a new but morphologically different cycle of vegetative growth. 

 This is especially true of fruits of the succulent, juicy type such as tomato. 

 The formation of the cells characteristic of such organs is usually favored 

 by a relatively high proportion of nitrogenous foods. The proportionate 

 amount of carbohydrate and proteinaceous foods which favors the best de- 

 velopment of fruits undoubtedly varies greatly, however, with different species. 



