GROWTH SUBSTANCES FOR OTHER PHENOMENA 119 



Tumor Formation. — Growth substances not only function by 

 regulating normal growth but also, under certain conditions, 

 bring about abnormal swellings and intumescences by hyper- 

 trophy of the tissues of stems and leaves. Cholodny (1931a, e) 

 placed coleoptile tips laterally upon the root tips of maize. 

 He found that tumor formation occurred and that the zone of 

 elongation of the swollen roots was significantly shortened. 

 Anatomical investigation revealed considerable enlargement of 

 the cortex. The number of cell layers was not changed, but 

 radial and tangential dimensions of the single cells were remark- 

 ably increased, and they were less susceptible to dyes than normal 



root cells. 



According to Loeb (1924), callus formation occurs only at the 

 basal, never at the apical, end of a stem of Bryophyllum. A 

 small piece of stem without leaves forms little or no callus, while a 

 piece of stem of the same mass with a leaf attached to it forms 

 considerable callus. 



Callus formation has been found to result from the application 

 of lanolin paste containing an extract obtained from orchid 

 pollinia (or human urine) to the internodes of Tradescantia and 

 Coleus (Laibach, Mai, and Muller, 1934). The active agent, 

 supposedly promoting cell division, was termed meristine. Since 

 it was found to be soluble in ether and water and is thermostable, 

 it was considered identical wdth auxin. Laibach and Fischnich 

 (1935a) devised a quantitative method of testing the callus- 

 forming action of 3-indole acetic acid paste (and other substances) 

 which brings about an increased rate of cell division in Vida 

 Faba epicotyls (Fig. 18A). Laibach (1935) reported that urine, 

 pollinia, and corn-flower pastes, when applied to decapitated 

 Vicia Faba epicotyls and to Coleus stems, all brought about callus 

 formation in 3 days. 



Czaja (1935c) has criticized Laibach's conclusion that a cell- 

 division effect has been demonstrated for growth substance in 

 callus formation. He found that if the growth substance is 

 apphed on the side of the axis so that it moves inward in opposi- 

 tion to the normal stream of the substance, swelling results below 

 the place of its application. These swellings arise by the trans- 

 verse stretching of the cells. Complete disorganization of the 

 normal polarity leading to cambial activity and the subsequent 

 formation of masses of tracheids on the apical end of the organ 



