44 



must be applied before the cells have reached their full size. Thus, 

 though in Cucurbita pepo several hypocotyls were put into casts, the 

 middle of the pith was in no case kept alive to the time of the first 

 examination, evidently because the cells had nearly reached their full 

 development when the experiments were begun. In Caltha palustris 

 the same condition was found; and one stem on being taken from 

 the cast showed much of the pith dead but uncollapsed, demonstrat- 

 ing that the pith had here died without suffering the usual amount 

 of tension from the cortex; for normally the pith is fully collapsed 

 by the tearing which it suffers. In Melianthus major where it is im- 

 possible to apply a cast long before the middle pith-cells die, such 

 cells have not been kept alive up to the time of the first examina- 

 tion from the cast though the growth of the shoot meanwhile was 

 only 2 cm in length. In Myrrhis odorata precisely the same relations 

 were found as mentioned for Caltha. In Archangelica sativa, Lamium 

 garganicum, Urtica dioica, Ricinus communis and Vicia faba the entire 

 pith has been kept alive for periods varying from 2 to 8 weeks after 

 it would normally have died. The development in these periods can 

 be found by referring to the record of the experiments. Suffice it to 

 say Dahlia and Vicia have been longest in cast, the former for 4 months, 

 the latter for 59 days without any dead pith appearing within the 

 gypsum in any individual. Dahlia however had not grown very well 

 in this time, but Vicia had reached the height of a meter and bore 

 blossoms. In both species the pith had died above and below the 

 casts , and it is certain that in the case of Vicia the pith had lived 

 within the cast 8 weeks longer than it would normally have done. 

 How much longer such a pith would live we have no means of know- 

 ing, but it does not seem impossible to think of it as continuing 

 till the death of the plant in autumn, — not merely because it has 

 not been injured by the growth of surrounding tissue, but it is pos- 

 sible that the plant as a regulatory means for meeting the exigency 

 induced by the cast may put the pith to a new use, such as aiding 

 in transport through the very narrow isthmus connecting the normal 

 parts of the stem. Such a regulation would be similar to that dis- 

 covered by de Tries 1 in a flower-stalk of Pelargonium zonale which 

 bore a vegetative bud among the blossoms. The flower-stalk instead 

 of dying in the usual way lived to function as a vegetative stem. 



Many of these preparations that showed a living pith in the 

 upper part of the casts presented more or less dead pith in the lower 



1 De Vries, Ueber abnormale Entstehung secundarer Gewebe. Jahrb. f. wiss. 

 Bot. Bd. 22. (1891.) 



