80 PHYTOHORMONES 



with auxin 101.3 per cent. The auxin thus produced only 

 a 9 per cent increase in the de-seeded against a 63 per cent 

 increase in the intact plants, so that growth of the de-seeded 

 plants was being almost entirely limited by the food factor. 

 A simple demonstration that growth of the upper part of 

 a coleoptile is limited by a factor other than auxin may be 

 given by applying auxin paste of low concentration to one 

 side of the extreme tip of an intact coleoptile. The first 

 visible curvature appears 6-10 mm. below the tip, showing 

 that the upper part of the plant does not respond to the 

 applied auxin; this must be because auxin is here in excess 

 and the food factor is therefore limiting (u). 



C. The Limitation of Size in the Plant 



In the preceding pages certain cases have been discussed 

 in which auxin is not the factor limiting growth. Laibach 

 and Kornmann (1933a), who were the first to apply auxin 

 to intact Avena coleoptiles, obtained with it only a tem- 

 porary increase in growth rate, the treated plants being 

 very soon caught up again by the controls. They therefore 

 drew the same conclusion as had Cholodny (1931a), that 

 auxin "appreciably accelerates the rate of development 

 and (correspondingly) shortens the duration of the life 

 cycle of each cell." In other words, if we hasten the growth 

 rate by appljdng auxin we also hasten the onset of maturity. 

 This view is the opposite of that of Went (1928), that ''the 

 mature state of a cell is only conditional; cells do not attain 

 any absolute final length, but their cessation of growth is 

 the result of a complex of circumstances." There are no 

 facts, nor any a priori reasons, for assuming that growth 

 is an autonomic function of a young plant cell, and that 

 the action of auxin is only to accelerate this primary growth. 

 In this monograph we have subscribed to the simpler view 

 that auxin is one of the many factors necessary for the 

 ordinary growth process, and "without auxin no growth." 



It is important, also, that in some cases excess auxin, 

 applied to intact plants, has definitely caused growth 



