CHAPTER XXXI 

 REPRODUCTIVENESS AND SEED GERMINATION 



Say which grain will grow and which will not. 



— Macbeth. 



Vegetativeness and Reproductiveness. — Why plants reproduce 

 when they do and the conditions which determine whether a 

 plant will develop vegetative structures (stems and leaves) or 

 reproductive organs (flowers and fruits) has long been a matter 

 of study. It was held for many years that there was something 

 incompatible between vegetativeness and reproductiveness; the 

 plant could not produce both shoots and fruits and must conse- 

 quently be either vegetative or fruitful. It was also thought that 

 the responses were more or less according to the needs of the plant. 

 If conditions were favorable for the growth of the individuals, 

 then the species was not in danger and reproduction would not 

 occur. If, however, conditions became unfavorable for growth, 

 it was "high time" to consider the species. The plants then "got 

 busy" and provided for the perpetuation of the species before 

 dying. These were the ideas in vogue until the work of Kraus 

 and Kraybill (1918), confirming earlier hypotheses of Klebs, 

 placed the matter upon a firmer basis. Working with tomatoes, 

 they showed that the kind of growth depends upon the relation 

 of the carbohydrates to the nitrogen compounds present in the 

 plant. With neither nitrogen nor carbohydrates, the plant neither 

 grew vegetatively nor reproduced. When the carbohydrates were 

 not too scanty, an excess of nitrates over carbohydrates resulted 

 in vegetative growth but no reproduction. As the carbohydrates 

 increased in proportion to the nitrates, there was an increase in 

 fruiting and a decrease in vegetative growth. The reproductive 

 and the vegetative growth may thus be controlled at will, depend- 

 ing upon the balance between the nitrogen compounds and the 

 carbohydrates. 



These results agree with experience. Fertilizers rich in nitrates 

 tend to increase vegetative growth and to check reproduction. 

 The carbohydrates stored in the plant during the summer's growth 



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