a BOTANICAL GAZETTE [APRIL 
TABLE D 
SEASONABLE SNOWFALL IN INCHES 
Sept. | Oct. | Nov. | Dec. Jan. | Feb. |March| April | May | Year 
Sunt ees a 6.2| 38.7| 52.2} 166.2] 47.2] 62.0) 23.5] 12] 408.0 
Parmarack 05. 5..-: 1.0} 16.6) 55.1] 60.5} 198.7) 76.2) 51.5] 36.5 18) 496.1 
Life zones 
TRANSITION ZONE.—The problem of attempting to discover the 
zonal limits of the various species collected in the Tahoe region is 
complicated by the very irregular topography; the line between 
adjacent zones is nowhere clearly defined, and, where the relief is 
especially rugged, often becomes very tortuous. Mapping can 
only express the general distribution, at least on maps of such a 
scale as are available. In addition to the complication caused by 
the relief and consequent frequent change of exposure, the soil 
characters cause a variableness in the zone boundaries; on the 
dark chocolate colored trap lives a flora whose members are dis- 
tinctly more xerophytic than those of granite soils. A very evi- 
dent change of plant life, for which this edaphic factor seems the 
only one assignable, is that found on the ridge connecting Suzy 
Lake with the mountain group culminating in Dick’s Peak. The 
ridge runs northwest to southeast and the south slope is fairly even, 
but where the trail runs out of the granite into the trap a break 
in the general aspect of the flora occurs: typical Upper Transition 
on the granite with Abies concolor and Pinus Jeffreyi as the chief 
trees, and Canadian on the trap with Juniperus occidentalis giving 
the tone to the forest. 
Another more difficult factor in the problem of assigning plants 
to definite zones is the fact that the plants often refuse to be s0 
assigned; the stragglers from the general rank are too numerous. 
Yet in spite of this it seems desirable and feasible to group the 
vegetation within certain altitudinal categories and, while many 
individuals of a given species will be often found outside the zone 
of their greatest frequency, as a whole the assemblage of plants 
denominated the “Transition flora of the Sierra” has a general 
coherence, and the expression conveys a definite meaning to those 
who have considered the whole Sierran flora. 
