A PRELIMINARY INQUIRY INTO THE SIGNIFICANCE 
OF TRACHEID-CALIBER IN CONIFERAE 
PERCY Groom . 
In connection with an investigation of the structure of the sec- 
ondary wood of Indian species of Pinus, conducted by W. RusHTON 
and myself (2), it seemed to me that some points of interest might 
be revealed by an inquiry into the relation between habitat and 
systematic affinity on the one hand, and, on the other, width of 
tracheid as measured in the spring zone. Fortunately, a compre- 
hensive list of measurements of the diameters of such tracheids in 
American Coniferae is given by PENHALLOw (4). These, together 
with the measurements made by Rusuton on Indian pines, serve 
as the basis for the succeeding discussion. 
In framing conclusions regarding the significance of the statis- 
tics, there are a number of points of difficulty that can be removed 
only by further research or by information supplied by American 
botanists and foresters. And it is partly in the hope of exciting 
such research that this tentative inquiry is published. The diffi- 
culties are: 
: 1. The caliber of the spring tracheids of a species varies in the 
Same annual ring with height above the ground, and in different 
annual rings at the same level. 
2. The caliber of the spring tracheids also varies in one and the 
same species according to the habitat in which the individual tree 
8rows. A number of American species of Pinus and other conifers 
Show considerable diversity in the habitat (edaphic and climatic) 
of the one and the same species. 
Possibly one of the two causes above mentioned accounts for 
the discrepancy between PENHALLOW’s measurements and mine in 
fonnection with Pinus glabra. 
3. Information as to the exact climate (rainfall and atmospheric 
humidity) of various habitats of species is lacking. 
4. Information as to the exact edaphic conditions, and particu- 
larly as regards amount of moisture and level of the water-table, 
287] [Botanical Gazette, vol. 57 
