1914] GROOM—TRACHEID-CALIBER 295 
require a. higher rainfall, so if narrowness of spring tracheids be a 
form of protection against desiccation, cold temperate pines might 
be able to afford to have wider tracheids than warm temperate 
growing in equally dry situations. P. Banksiana (43 pw) has nar- 
rower tracheids than P. resinosa (44m), which usually grows in 
less dry places. These two species are accompanied often by the 
haploxylic moisture-loving P. Strobus (41.5 m), whose spring 
tracheids are narrower, just as is the case with the haploxylic 
P. Lambertiana compared with its diploxylic occasional companion, 
P. Jeffreyi. 
The remaining species, excepting P. Jeffreyi, are subtropical 
Atlantic, occurring near the coast in a region where there is a heavy 
rainfall] during summer and winter, and the air is moist. It is sig- 
nificant that in this group of pines possessing the widest spring 
tracheids, these latter agree sufficiently in diameter whether the 
species belong to the section TAEDA or to PrvasTeR. First, there 
are two, one belonging to each section, with a diameter of 44 u; 
then there are four belonging to TaEDa, two with the diameter 47 y, 
and two with 49 w and 49.5 m, respectively. Lastly, there are two 
belonging to PrnasTEr, with the diameter of 48 ». The species that 
1s the most clearly tropical in distribution is the one having the 
Widest spring tracheids; and such is likewise the case in India where 
the tropical P. Merkusii grows on sites receiving, at least periodi- 
cally, very considerable supplies of moisture. 
_ Ifagain we range the species in accordance with Mayr’s group- 
ing as subtropical, warm temperate, cool temperate, and alpine, in 
order so far as possible to determine temperature as a factor, the 
following facts come out. 
Subiropical—The five diploxylic species (nos. 2, 5, 10, 13, 14 in 
table II), characterized by narrow spring tracheids ranging from 30 
t0 40 p, are all Pacific species, with or without marked perviousness 
of soil. The remaining diploxylic species (nos. 17, 18, 19, 21, 23, 
24, 25), having wider spring tracheids, are Atlantic species living in 
moist climate. The Pacific and Atlantic groups both include 
representatives of the sections TAEDA and PINASTER. 
arm temperate—The first six diploxylic species, with the nar- 
TOwest spring tracheids ranging from 29.5 to 38.5 #, include two 
