36 



III. DISCUSSION. 



1. Effect of gypsum casts on the functional activity of 

 meristematic tissue. 



Without exception the plants that have been under experiment 

 have shown , when a cast has been put around the stem near the 

 apex, a resting period lasting from a few days to many weeks. 

 Some plants will rest much longer than others, but even in the same 

 species the period varies greatly in duration. Vicia faba rests but 

 a few days; Cucurbita pepo from a few days to a few weeks; two 

 plants of Helianthus tuberosus have shown no growth anywhere , the 

 one for 8 weeks, the other for 10 weeks, but are still living; while 

 Dahlia variabilis, which rests usually for a week or more, gives one 

 example where there has been cessation of growth for 15 weeks, 

 but in which active development recommenced on exposing the plant 

 to the full day's direct sunlight. In the two cases last mentioned, 

 control plants in the same pots made very good growth, the Dahlia 

 contral plant reaching the height of nearly a meter, while the one 

 in the cast remained at the height of 15 cm , though both were the 

 same size and age when the cast was applied. 



The case of J uncus ,effusus and Allium cepa was somewhat different 

 where the whole growing shoot was encased in gypsum. The results 

 are comparable with those obtained by Pfeffer in a work not yet 

 published, but some pages from the manuscript of which he kindly 

 permitted the author to read, where Spirogyra and the growing root- 

 tips of several plants after lying for weeks in gypsum casts grew 

 farther on being removed from the casts. 



Many young shoots, 2 cm or 3 cm in length, of Juncus were wholly 

 encased in gypsum, and examined after different periods of time, the 

 longest period of confinement being 11 weeks. In all cases the 

 young shoots were still living, showing the peripheral band of living 

 cells wider than usual, but otherwise no change during their enforced 

 cessation of growth. Whether such shoots would grow after release 

 from the cast was not determined experimentally; yet from the 

 behaviour of other plants under similar treatment there can be but 

 little doubt that the growth would be resumed and would progress 

 normally. 



The 3 germinating bulbs of Allium cepa were also so encased 



