14 BULLETIN 1059, U. S. DEPARTMENT OF AGRICULTURE. 
to germination and development of the small and very sensitive 
seedlings. The forester is often concerned only with the problem 
of " securing reproduction." realizing that, once the seedlings of a 
given species are established, the future of the stand is quite 
definitely assured and practically beyond his ability to influence. 
In forestry particularly, because perennial plants are the subjects of 
study, the seedling stage presents the most acute practical problems 
and those most deserving of scientific study. What bearing this 
has on the methods to be followed in ecological investigations may be 
readily illustrated. If. for example, it should be noted that seedlings 
of a given species die in great numbers during their first or second 
winter and it is desired to determine why such losses occur and 
whether they are preventable, it might be deemed necessary to study 
the rate of evaporation and the amount of drying to which such 
seedlings are subjected during periods when the soil is frozen. Obvi- 
ously, it would be necessary to determine this period precisely and 
to know (1) when the soil was frozen throughout the root zone of 
the seedlings, and (2) when it was frozen at the surface so that 
moisture obtained below might not reach the aerial portion. On 
the other hand, the atmospheric stresses and the tendency toward 
evaporation losses generally might be measured, that is to say. for 
the locality and at a convenient spot : but it would be apparent that 
if the seedlings under observation were covered by snow the rate 
of evaporation above that snow layer would have no significance 
whatever. 
The point, therefore, needs the greatest possible stress that, in the 
investigation of many of the particular problems of reproduction and 
distribution of the species, the investigator must be concerned with the 
immediate condition- of the surface soil and the atmospheric and solar 
condition- at an elevation barely above the surface soil, in connection 
with germination, with survival before the seedling becomes well 
rooted, and with possible injury through heat or drought at the soil's 
surface before the young stem is protected by an effective corticle. 
Measurements at depths of even 1 foot in the soil, or at elevations of a 
foot above it. will usually only be made to give general, comparative 
indications of the conditions which it is really neces-ary to under- 
stand: and because the rapidly fluctuating conditions of the soil's sur- 
face are in many ways extremely difficult to cope with. 
In considering the conditions which affect reproduction, an eleva- 
tion of 6 inches above the surface may possibly be accepted as the 
lowest level at which aerial measurements are practicable, but by the 
exercise of ingenuity it should be possible to improve on this. In soil 
study, greatest attention must be paid Vo the near-surface conditions. 
The actual moisture of the covering of litter and humus, as well as 
that of the first mineral soil, is obviously important, but extremely 
