220 STUDIES IN PLANT REGENERATION 
Experiment 36. — Euphorbia nivulia is а xerophyte which 15 
leafless except at the growing apex. Іп the plants that have 
been under observation in the greenhouse, moreover, these new 
stems bear leaves for only a few months in the year. When 
planted, however, the leaves lived for over fifteen months in the 
sand. Ағ the end of that period, while still in a healthy growing 
condition, they were transferred to a pot of fertilized soil in an 
attempt to induce shoot-formation. Very shortly after the transfer 
the entire pot and its contents unaccountably disappeared. 
Experiment 37. — Muhlenbeckia platyclados also has leaves 
which are found only in the “juvenile” condition and form part 
of the plant for only a very limited period (see Fig. 7) Yet upon 
being placed in the sand, they also rooted and maintained them- 
selves for several months, though not so long as Euphorbia nivulia. 
Küster* makes a statement that thick leaves form calluses 
very readily, as a rule, while thin leaves or those containing a 
great deal of water usually produce only a very weak callus. For 
this reason, he continues, cotyledons usually are richer in this 
respect than later leaves. This has not proved to be the case with 
the leaves of the kidney bean (Phaseolus vulgaris), lima bean 
(Phaseolus lunatus) or lupine (Lupinus alba). The primary and 
later leaves of the bean, which are very thin, form a larger callus 
and root more easily than any other leaves which have been tried. 
Their regeneration takes place with considerably more certainty 
and rapidity than that of the cotyledons, which very frequently 
decay without forming calluses or roots. The lupine cotyledons 
also form weaker calluses and regenerate more slowly than the 
later leaves. 
The leaf of the bean forms a callus within a few days after 
being planted, and roots develop between the ninth and the thir- 
teenth day. The question as to the point of origin of such roots 
has been much discussed. Stoll,t disputing a statement made by 
Crugeri that roots could arise either in the callus or above it, 
maintained that the callus formed no vegetative points, but that 
С *Klster, E. Pathologische Pflanzenanatomie 168. 
L L 1203, 
tStoll, В. Uber die Bildung des Kallus bei Stecklingen, Bot. Zeit. 32 : 736. 
4. 
t Cruger, Н. Einiges über die Geweberinderungen bei der Fortpflanzung durch 
Stecklinge. Bot. Zeit. 18 : 369. 1860. 
