I. METHODS. 



In the present work the effort -has been to arrest the radial and 

 longitudinal extension of primary growth, by the application of me- 

 chanical resistance with as little injury to the plant as possible. The 

 means to effect this end has been the application of gypsum casts 1 . 



When a plant organ was to be encased an envelope of stiff paper 

 was fitted around the object, and a thick mixture of gypsum and 

 water poured into the mould. The diameter of the cast varied accord- 

 ing to the size of the organ encased, but was nearly always of such 

 a size that it needed support other than that given by the plant, 

 since experience taught that casts several times the diameter of the 

 organ encased might be sprung. 



The length of the plant segment enclosed in gypsum has varied 

 between 3 cm and 10 cm . A shorter cast than 3 cm could not be depended 

 upon to give intelligible results, since it had been found that near 

 the limits of the cast the behaviour of the part enclosed is quite differ- 

 ent from what it is well within. It is certain that by confining the 

 growth of an organ for the length of but a centimeter or two, results 

 would be obtained very different from those here presented. 



To control the results found in the parts grown within casts, 

 corresponding parts have been kept within opaque wrappings, and 

 numerous comparisons have been made with normal plants. 



II. EXPEPvlMENTAL PART. 



The objects for the experiments have with 2 exceptions been 

 stems, and in the majority of cases such stems as become hollow 

 during primary growth. The structure which the organs have had 



1 Pfeffer has used this method in researches for some time and has described 

 it in Berichte d. k. slichs. Gesellsch. d. Wissenschaften, December 1892: Ueber An- 

 wendung des Gypsverbandes fur pflanzenphysiologische Studicn. 



1* 



