26 o 
Holmes. — A Contribution to the Study of 
apex in each first-year segment, steeper as usual towards its beginning. It 
will be seen from Figs, i, 2 , 5, and 10 that in S3 the annual additions to the 
plant were shorter and thinner than in S2 and S4. The water-conducting 
area in this wood is indicated in Curve B, which gives the total area in mm. 2 
of the lumina of all the water-conducting elements in the transverse section 
of the wood at each internode. This also shows a simple decline from the 
base to the apex of each shoot in its first year, somewhat flatter towards the 
end ; it corresponds to the simple successive decreases in the number 
of leaves supplied, the upper ones being smaller than the lower ones. The 
total number of the water-conducting elements in each section, as shown in 
Curve F, reveals again a decline from base to apex, but there is a tendency 
towards a marked flattening, or even a rise, quite close to the end, Figs. 3, 
4, 10, and 1 1 . These elements, however, are particularly small, as shown 
by the steeper decline of Curve E, which gives the average diameters of their 
lumina in /x, towards the end of each first-year shoot. The vessels of large 
diameter occur in the lower part of the shoot, where the average diameter 
falls quite slowly, while they are absent from the apical part. The distri- 
bution of the conducting elements may be inferred to some extent from 
Curve D, which shows the number occurring per square millimetre in the 
transverse section of the wood in each internode ; the line rises gradually at 
first, and then with increasing rapidity towards the end in each first-year 
