268 BOTANICAL GAZETTE [APRIL 
growth of a tubercle is evidenced by the fact that they may 
be seen forming very near the tip. To determine whether 
these structures are really lenticels, air was forced through 
the tubercles under water by means of an aspirator. The 
streams of air which were given off indicated that the struc- 
tures are lenticels in function as well as in form. It might be 
inferred, therefore, that the so-called tubercles are used in aera- 
tion, but this would seem to be but an incidental result of their 
structure. It has been shown by Jost‘ that plants deprived of a 
sufficient supply of oxygen develop air conducting tissue and 
abnormal growths, and it is possible that this represents the con- 
dition of Cycas. 
Upon comparing the general structure of the tubercle-like 
rootlets with those which are normal, it is to be noted that the 
tubercles have round tips which do not possess a true root cap. 
Instead of the conical root cap of the normal root they have a 
sheath of several cell layers extending over the tip and also 
enveloping the entire tubercle as an outer cortex (fig. 3). No 
such cortex is developed in the normal root. 
In studying the fungi and bacteria of the tubercles, cultures 
were made on agar. From these cultures at least three bac- 
terial forms and an organism resembling the Rhizobium of 
Schneider’? were obtained (jigs. 7, 8). The bacteria included 
one very large form, a small chain-like form, and a coccus form. 
The hyphae of fungi were also observed in the cells of the 
tubercles just in advance of the algal zone (fg. 9), but they 
were not in a condition to be identified. In fact, a zone of dif- 
ferentiated cells extends from the algal zone to the meristem of 
the tip (fig. 3), the cells being shorter than the. adjoining cells 
and their contents more granular. 
The fungi and bacteria which are in the cells in advance of 
the algal zone seem to prepare the way for the algae (fig. 0), 
since their presence seems to result in very much enlarging the 
small intercellular spaces, which become the relatively large 
‘Ein Beitrag zur Kenntniss der Athmungsorgane der Pflanzen. Bot. Zeit. 45 °37— 
39. 1887. 
