201 
SKETCH OF THE GROWTH FOR ONE YEAR. 
Libriform, with ¥ satan 
CAMBIUM. 
ig 
bordered pores. 
Libriform, with 
simple and bordered pores. 
Libriform, with 
only simple pores. 
| | 
aed§ Libriform, with ‘ 
2 simple and bordered pores. 
| 
Trachez and tracheids. 
s Spring wood, with 
: only few libriform cells. 
The cells first formed from the cambium in the spring lie 
next to the inner limit of the annual ring (see @), and consist of 
large trachez and thin-walled tracheids with large bordered pores. 
Next follows zone 4, in which the tracheze and tracheids are 
much smaller in diameter, and the walls of the tracheids per- 
ceptibly thicker. In zone c, only a few trachee occur; the 
walls of the tracheids here are nearly as thick as in the real libri- 
form cells, and contain bordered pores which diminish in size and 
frequency toward the middle of the year’s ring or the summer's 
growth. Then follows the zone d, which consists almost entirely 
of thick-walled, simple-pored, libriform cells. This zone varies 
in size; in the sections examined it averaged between 4 and 4 
of the whole width of the year’s ring. Then follows another 
zone, é, where the bordered pores again appear, of about the same 
size and frequency as in zone c. Lastly comes the autumn- 
wood, f, in which the pores are all bordered ; they lie mostly on 
the tangential walls, but are not restricted to these; the borders 
are quite large, often reaching the size of those found in the 
thin-walled tracheids. 
To explain the supposed adaptation here to the transfer of 
water at such times when the need is greatest, we refer once 
more to the coniferous woods, with which experiments have been 
made which verify some of the assumptions regarding the water 
transport, and furnish a kind of centre around which may be 
grouped other facts and conjectures. It is well known that the 
pores of the tracheids of the summer wood of the conifers lie on 
