98 The Phenomena of Morphogenesis 



early plant size. Passmore (1934), working with reciprocal hybrids be- 

 tween large-seeded and small-seeded cucurbits, and Oexemann (1942), 

 with several vegetables, observed that plants from large seeds have an 

 initial advantage in size because of the larger amount of food stored in 

 the seed but that this usually disappears after a time. 



Similarly, in vegetative propagation the size of a "seed" piece in pota- 

 toes, though it may influence early sprout growth, has no effect on yield 

 (Wakanker, 1944), though if the bigger pieces have more buds on them, 

 sprout number will be larger and yield somewhat increased. 



A positive correlation between the size of a fruit and of the seeds in it 

 has often been found, as by Schander (1952) in apple and pear and by 

 Simak ( 1953 ) for seed size and cone size in pine. In fruits and cones of 

 the same size, however, seed size was inversely proportional to seed num- 

 ber. Both nutritional and compensatory correlations are probably in- 

 volved here. 



Ashby (1930) suggested that the larger plant size resulting from 

 heterosis was due to greater size of the embryos that produce the heterotic 

 plants, thus giving them an initial advantage which was maintained 

 throughout growth. Present evidence, however, does not support this idea. 



Compensatory Correlations. The nutritional factor in the relation be- 

 tween two parts of a plant may be evident in other ways than by transfer 

 of food from one to another. Each growing part or organ constitutes what 

 Goebel called an "attraction center" which under normal conditions draws 

 to itself a specific amount of building material. This may be small or large, 

 depending on its genetic constitution. In one of the higher plants, 

 which has many similar growing parts such as leaves, flowers, and fruits, 

 the number of these parts may be reduced by accident or experiment. In 

 such cases there is often a compensatory increase in the growth of the 

 remaining structures, so that a negative correlation results between the 

 size and the number of parts (Lilleland and Brown, 1939). Thinning of 

 fruits by mechanical or chemical means is sometimes practiced so that 

 the remaining fruits will grow larger. In the same way, the removal of all 

 buds but one in a certain type of chrysanthemum results in the develop- 

 ment of this single flower head, through compensatory growth, to a size 

 very much larger than normal. 



The reverse of this relationship also may occur, for if many fruit are 

 set, they will be small. In such cases, some may drop off. Thus in apples 

 there usually occurs a "June drop" in which many of the young fruit, 

 unable to attract to themselves a sufficient supply of food or auxin, stop 

 growing and are cut off by abscission layers. In a somewhat similar way, 

 the more seed developing in a tomato fruit and the more fruits in a 

 cluster, the smaller will be the weight of each seed (Luckwill, 1939; 

 Schander, 1952; and Simak, 1953). 



