634 Hunter. ~ The Aerating System of Vida Faha. 
Summary. 
1. The testa of the bean is composed of three definite layers: 
(a) An epidermis of thick-walled cells. 
(b) A single layer of pillar-shaped cells. 
(c) Parenchyma. 
Intercellular spaces form a prominent feature of ( b ), they are present in (<:), 
and absent in (a). 
2. The cotyledon of the bean is permeated by a continuous aerating 
system ; stomata are absent. 
3. The central air-cavity of the stem of Vida Faba is not uniform in 
cross section. In the youngest internodes it is much divided, in the central 
internodes it takes on a circular form and reaches its maximum develop¬ 
ment, and in lower internodes it is reduced until it finally disappears. 
4. The division of the air-cavities in the youngest internodes is 
probably a means of securing a sufficient gaseous exchange in the active 
region of the growing point. 
5. The small air-cavities of the youngest internodes are of schizogenic 
origin. The transformation of these into one central air-cavity is of 
a lysigenic nature. 
6 . A ring of lysigenic cavities is present in the cortex of the oldest 
internodes. 
7. It is suggested that the production of these cortical air-cavities 
is a device to assist in the respiration of the cortical cells of the old root. 
8. The intercellular spaces in the ground tissue of the stem are originally 
triangular in cross section. The fusing of two or more of these results in 
more complex forms. 
9. The palisade cells of the leaf are separated by large intercellular 
spaces. 
10. The intercellular space system of the root-tip forms a very 
important feature of a longitudinal section, and clearly demonstrates that 
the aerating system is of the utmost importance in the most active regions 
of cell development. 
In conclusion, the author’s thanks are due to Dr. Darbishire for the 
kind interest which he has taken in this work. 
The University, 
Bristol. 
