TENOPYR: CONSTANCY OF CELL SHAPE 59 
when the illumination is stronger and the plant already possesses 
a well developed root system and numerous basal leaves, that the 
narrow stem leaves and flowers appear. Even then, a diminution 
of the light intensity, or any great disturbance in the development 
of the plant can occasion the production of the juvenile form of 
leaf. Thus, if the Campanula plant is propagated by cuttings from 
shoots bearing only long narrow leaves, the young leaves sent out 
by these plants are round, like the basal leaves of the parent plant. 
These propagated plants cannot produce long leaves until they 
have better developed root systems, and the plants have become 
well established in their new food relations. 
I have studied the shape, i. e., the relation of length to breadth 
of leaves and their constituent cells, in the following three types of | 
plants. 
I. Species with broad basal leaves, narrow stem leaves near the 
inflorescence, and transitional leaves on the lower part of the stem: 
Campanula rotundifolia, Lobelia Erinus. 
2. Broad-leaved and narrow-leaved species belonging to the 
same genus: Plantago major and P. lanceolata, Linum angustifolium 
and L. usitatissimum. 
3. Varieties of the same species having entire leaves, as com- 
pared with others having lobed leaves: Cichorium Intybus. 
METHODS 
The Schwendener-Ambronn method used by Sierp, which gives 
the average area of the cells, was not suited for my investigations 
on the relation of the length to the breadth of the cells of variously 
shaped leaves. The method used in finding the average length 
and the average breadth of the cell resembles that of Amelung, 
except that an ocular micrometer instead of a stage micrometer 
was used. The number of cells to a unit of the scale in the ocular 
micrometer were counted, and the average dimensions in milli- 
meters were estimated from these numbers. Whenever the line 
of measurement passed through the two opposite sides of a cell, 
as it appeared in the section regardless of how small a fragment of 
the entire cell was thus cut, its measurement was recorded as the 
measurement of the length or of the breadth of the cell in that par- 
ticular portion of the leaf. If, as sometimes happened in the 
irregular cells of the epidermis, the same line ‘passed twice through 
* 
