PETRY: VEGETATION oF NEW York STATE 209 
species of the association spread readily by vegetative propagation, 
but ripe spores or seeds are also produced by most of them. On 
the other hand, the short season cannot be effective in preventing 
the invasion of plants of the higher parts of the slope, since these 
species have a longer season in which to mature spores or seeds, and 
every facility for their distribution into the bottom area. 
With regard to the temperature conditions, however, the case 
is different. Casual observation indicated that the characteristic 
species of the bottom association do not occur outside the region 
of noticeably low temperatures. To verify this observation the 
Fic. 3. Map of plunge basin showing distribution of Ribes lacustre (Pers.) Poir. 
tin. = 160 ft 
exact distribution within the basin of five of the dominant species 
was determined and plotted. The maps of the distribution areas 
are remarkably alike; that for Ribes lacustre, given in FIG. 3, is 
typical. By comparison with Fre. 1 it will be seen that the dis- 
tribution area is only roughly that of low air temperatures, being 
extended farther along the axis of the basin. A comparison of 
Fics. 2 and 3, however, shows a remarkable similarity between the 
outline of the distribution area of Ribes and the soil isotherm of 
56° Fahr.; and the maps of the distribution areas of the other species 
show an equally close resemblance. This coincidence of the areas 
of low soil temperature and of distribution of five of the dominant 
