8i 
upon the Size of Leaves. 
Apart from an apparent very slight increase in breadth which might 
easily be due to a greater divergence of the leaf teeth, or to a flattening of 
the lamina, no increase in size is shown. 
The second branch had an erect glass tube filled with water attached 
to a side branch near to the apex, and on this branch and ultimately on 
a neighbouring one, a new surface was cut every second day for the entry 
of water. It was not found possible to maintain a greater pressure than 
io ft. of water, since beyond this pressure the water passed backwards 
rapidly into the main trunk. A pressure of from 6 to io ft. was, however, 
maintained for a month, and the measurements in brackets were taken on 
August 30 : — 
Lamina. 
Petiole. 
1st leaf 
2-3 (2-4) 
2nd leaf 
2-9 ( 2 - 9 ) 
3rd leaf 
3'3 ( 3 ' 5 ) 
4th leaf 
3-3 ( 3 - 5 ) 
5th leaf 
3 -° ( 3 ' 1 ) 
Breadth. 
Length. 
6-6 ( 6 - 6 ) 
7-5 ( 7 - 4 ) 1 
7-0 (7-0) 
8-2 (8-2) 
8.5 (8-8) 
TO-O (9-8) 1 
8.5 (8-6) 
11*2 (ll*2) 
7-8 (8-o) 
io-i (10-4) 
Internode. 
07 (o-8) 
i -5 (i\ 5 ) 
3-4 ( 3 ' 4 ) 
37 ( 37 ) 
Hence, neither the effect of an unusually abundant supply of water nor of 
the correlative influences due to the removal of the other buds and leaves 
are able to excite any renewed growth in an adult leaf of Tilia, even when 
acting conjointly. These influences, possibly aided by a more abundant 
supply of food, do, however, cause leaves to develop to an abnormally large 
size when applied at a sufficiently early period of their growth. The 
increased size is, however, not due to an increase in the size of the 
individual cells, but to an increase in their numbers. 
Thus in sections of a leaf measuring 13*2 X 16-8 and of one measuring 
6-i x 7*4 taken parallel to the midrib, the number of epidermal cells 
between the ends of a micrometer under the high power at various points 
was in both cases from 8 to 12, and of palisade parenchyma cells from 
20 to 35 - Similarly, the following numbers give the maximal divergences in 
the number of cells across the diameter of the high power field in transverse 
sections at various points of large and small leaves : — 
Size of leaf 17*1x12-5 3-5x3 
Upper epidermis 10 to 16 10 to 15 
Palisade parenchyma 35 to 52 38 to 48 
Lower epidermis 11 to 18 12 to 17 
At corresponding points on the two leaves the numbers agreed very 
closely. 
The facts first mentioned hardly agree with the usually accepted idea 
that the total number of leaf-cells is determined at an early date, and that 
1 Tip slightly withered. 
