20 BOTANICAL GAZETTE [JANUARY 
‘be a necessity. The possibility must be admitted that light (or 
rather radiant energy) is only indirectly the important factor, its 
influence lying in its effect upon the seed bed. Densely shaded 
soils upon Isle Royale are nearly everywhere more or less of the 
nature of peat, low in temperature, soggy with unavailable water, 
and probably like peat deficient in certain types of bacterial and 
fungal life. The obvious effects of abundant access of radiant 
energy would be to partially cure the sogginess of the soil and thus 
increase its oxygen content, and to bring about a high soil tempera- 
ture; both of which changes would result in greatly increased 
activity among the various types of soil organisms. Plans to 
carry out some experiments with a view toward determining the 
germination conditions of the balsam and other trees were frustrated 
by the total failure of the seed crop in 1910. 
A second cause, which easily accounts for a considerable viet 
of the young growth of balsam, is found in the habit of layering, 
by which that species reproduces abundantly. All the other coni- 
fers of Isle Royale except the pines possess the habit too, but to a 
much less degree. In a previous paper (12) I have described in 
detail the layering habit of the balsam and other conifers, and 
therefore a few words here will be sufficient. In the forest one 
frequently comes upon small groups of young balsams, composed 
often of about half a dozen individuals of various sizes. Upon 
superficial inspection these would easily pass for a cluster of seed- 
lings, but if the group be carefully dug up it will be found that the 
young trees are all connected with each other just below the surface 
of the ground. The group comes into existence in the following 
manner. One or more of the earliest branches of a young tree 
(which is sometimes hardly beyond the seedling stage) comes to be 
slightly covered with humus and litter, and produces roots. The 
tips then become erect, and taking on radial symmetry are trans- 
formed into miniature trees. By successive layering of branches as 
many as five generations produced in this manner may be included 
in a single group. Large drooping branches of mature individuals 
may layer in the same way, and it is not uncommon to find an old 
trunk surrounded by a circle of daughter trees developed from 
layered branches. The young shoots soon come to depend entirely 
