298 BOTANICAL GAZETTE [MAY 
the rapid evaporation from the loose soil. The soil heats up 
and cools off rapidly, so that the variation in temperature in a 
short space of time is great, a condition unfavorable to plant 
growth. Nevertheless, in spite of the strong insolation and dry 
soil, if sufficient time elapses a definite fossil beach society is 
obtained. The enumeration of species is not of any consequence. 
They are at first mostly herbs, both annual and perennial. By 
their death, and in some instances by the decay of old logs left 
by storms when the beach was nearer the lake, humus conditions 
of the soil are gradually obtained. This is at first slow because 
of insolation. Nevertheless, each year adds its growth of herbs, 
and even though a greater part is dried out or blown away, in 
time the better humus condition will bring about the possi- 
bility of a higher type of plant society, so the fossil beach 
society gradually develops into a heath. 
Heatu. The heath society is considered, in the normal 
development, the fourth stage in the life history of the forest. 
It will be well to keep in mind the changes that make possible 
the heath. These are the increase in the amount of humus and 
the element of time. Juniperus communis, J. Sabina procumbens, 
Arctostaphylos Uva-urst, Pleris aquilina, Zygadenus elegans, Solidago 
nemoralis, Campanula rotundifolia, and Comandra umbellata are 
some of the characteristic plants of the heath. /ig. z shows a 
heath at the foot of a coniferous forest on the lake side of a 
sand dune. 
Now for the first time biotic factors assume some importance, 
though slight. In the first three stages the struggle of plants 
against adverse physical conditions gave plenty of room for all 
able to survive. Although the physical conditions are still 
unfavorable, in places plants like the junipers and bearberry 
may occupy considerable areas to the exclusion of others. In 
the open spaces between the individual shrubby plants, however, 
there is sufficient room for a large number of herbs. These by 
decay contribute humus to the soil, and since the insolation is 
not so great as in previous societies, a larger portion of the 
decaying vegetation is prevented from drying out. Thus as 

