274 
Pearsall.—Studies in Growth. 
views put forward above. The author shows, in brief, that removal of the 
flowers or developing fruit permits a further development of stem elonga¬ 
tion. He suggests, however, that this is due to the downward movement of 
carbohydrates to the fruits. This involves the assumption of a correlating 
factor which causes the deflexion of assimilates from the apical region to 
the developing fruit. Two sets of facts demonstrated by Mason seem to be 
opposed to these assumptions. In the first place, the removal of vegetative 
branches causes only a slightly increased rate of axis elongation, while 
flower formation is increased by 50 per cent. Secondly, the correlation 
coefficients between neighbouring fruiting branches are greatest in the apical 
region. Both of these facts can, however, be readily explained on the 
assumption used in the preceding pages, that food supply from the roots is 
the limiting factor. In the latter case, the flowers would draw first on this 
supply and the removal of the vegetative branches would thus increase food 
supply to the flowers, allowing only the excess materials to reach the stem 
apex. Moreover, the farther the fruiting branches are away from the source 
of supply the more rigidly would their activity be limited by the food 
supply and the closer would be the correlation between successive branches. 
Summary. 
1 
1. Data are presented for the growth of roots from seeds, measured as 
changes of volume and of weight. 
2. The evidence shows that the development of subordinate roots upon 
roots of seedlings causes a temporary decrease in growth rate. The 
increase in the size of the root meristems after secondary root production 
appears to produce no corresponding increase in the growth rate of the 
whole root. The stem continues to grow after the root has stopped. 
3. The observed facts are consistent with the hypothesis previously 
developed that food supply is a limiting factor in the early periods of root 
growth from seeds and cuttings. The stem is assumed to compete 
successfully with the root for the cotyledonary food supply, especially after 
the development of secondary roots, thus causing a reduction of the root 
growth rate. 
4. The data of Balls and of Harland for growth of stem, flowers, and 
fruits in cotton are examined, as representing a case in which food supply 
from the roots is assumed to be a limiting factor. 
5. It is shown from these results that in cotton the decreased rate of 
growth of the stem can be attributed to flowering, and that subsequently the 
decreased flowering rate can be attributed to the development of fruits 
nearer the source of supply of the presumed limiting food factors. 
