44 The Ottawa Naturalist. [June-July 



intervenes so constantly during the earlier stages of seedling 

 development as to make it very difficult, if not impossible, to 

 grow the tree from the seed." The usefulness of the seed is 

 thus defeated. 



Again, many plants are unable to shed their leaves at all. 

 Eupatorium adenophorum, like a multitude of others, does not 

 do so in nature, nor, as found by Wiesner (1905, through Loewi), 

 even under experimental conditions. This disharmony is not 

 confined to herbaceous plants, as I have found it to occur in 

 the perennial shrub Parihenium argentatum. This plant, neither 

 in its native health nor under a variety of experimental con- 

 ditions, is found to lose its leaves save by a long delayed method 

 of wear and tear, somewhat hastened it may be by a clumsy 

 development of corky tissue continuous with that of the stem, 

 but developing first from a centre at the leafbase. (Lloyd, 8). 



Abscission of Shoots! 



Not a few trees are able to shed, by a process similar, if not 

 identical,* with that in leaves, their smaller, and in some cases, 

 even their larger branches. The Central American Rubber Tree 

 iCastilloa elastica) is a striking illustration, and has been 

 described by O. F.. Cook (9). The young tree produces no 

 permanent branches till the third or fourth year. Those which 

 develop before that time are long and semi-pendulous, measuring 

 scarcely one inch in diameter at the base and reaching a length 

 of ten or twelve feet. These are all shed, being released by a 

 softer laver of tissue, arranged in the form of a socket, quite at 

 their basal extremities. The loss of twigs by poplars, willows 

 and other trees is comparable with, if not as striking as, that of 

 Castilloa. The shedding of twigs produced from axillary buds 

 which grow at once, instead of entering a resting condition, 

 occurs in the camphor tree (in Alabama), which, in respect of 

 general appearance of the abscission, is very similar to Castilloa. 

 The mechanism of abscission in its living tissues (cortex) is 

 identical with that of the leaf, as v. Hoehnel observed in Popithts, 

 Salix, beech, etc., and as Loewi also found to be the case in 

 Cinnamomum Camphora. Euonyinus airopurptireus, Avhich is 

 grown in this part of the world as a small ornamental tree, also 

 sheds its twigs, more especially those which hajipen to be 

 exposed to the denser shade of overhanging branches. Loewi 

 observed this behaviour in potted plants, attribtiting it to too 



' Mv attention was drawn to this instance by my colleague, Profe.ssor 

 Willey. 'See Wright, H., Ann. Roy. Bot. Gard. Peradeniya, vol. 2 (?). 



*It is obvious that when large masses of wood, etc., are involved, 

 some sort of fragmentation must take place, but a really satisfactory 

 account of the underlying causes is not vet available. See, however, 

 y. Hoehnel, 10, 11. 



