136 PRODUCTION OF AIR PASSAGES IN THE ROOT OF ZEA MAYS. 
cylinder, and were roughly circular in section. They 
occupied a central position in the cortex. 
Fig. 3 is from a section of a root grown in this medium. 
(5) Wet Ashy Soil. —The roots were well developed and root 
hairs were present. The air-spaces were not constant in 
their occurrence, some roots being entirely without them. 
In others, however, there was a tendency to form them, and 
they were of the type found in potting soil. Many sections 
showed faintly denned groups of cells which rather seemed 
to point to the formation of air-spaces. 
(6) Ordinary Soil. — These roots were similar in nearly every 
respect to those developed in potting soil. The air-spaces 
were rather more frequent in their occurence. 
(7) Water Cultures. — Several cultures were made in water and 
various food solutions. In all cases the roots were long 
and stringy, and were developed in considerable numbers. 
In all these roots the air-spaces were very characteristic 
throughout. They were not confined to the centre of the 
cortical tissues, but were narrow, and stretched nearly from 
the epidermal layer to the central cylinder. 
There was a tendency for the central cylinder to become 
very compact. 
Fig. 4 is a typical drawing of the structure occurring in 
roots from water cultures. 
Conclusions. 
From these experiments it would seem as if the plant made a 
definite and immediate response to the variations in the external 
conditions. 
The development of air-spaces appears to depend largely upon 
the quantity of air available in the medium surrounding the root. 
In those roots grown in sand — which retains little water and 
allows a fairly easy access of air — the air-spaces did not appear to 
be necessary, and we seem to be able to trace a fairly definite 
series throughout the different roots. Those growing in water 
show the most complete system of air-spaces. In this case the 
whole cortex is of a very flimsy and indefinite nature, and is very 
apt to fall all to pieces when an attempt is made to section the 
roots. 
In other cases the cortex is more definite, and the air-spaces 
more regular in form and distribution. Further experiments with 
more definite methods of aeration of the medium will no doubt 
show a very, close relation between these air-spaces in the roots 
and the quantity of available air surrounding them. 
EXPLANATION OF FIGURES (Plates III and IV.) 
Fig. 1. Root Section of plant grown in Sand. 
Fig. 2. ,, ,, ,, ,, Damp Sawdust. 
Fig. 3. ,, ,, ,, Damp Clay Soil. 
Fig. 4. ,, ,, ,, ,, Water Culture. 
