5 16 
Shove.—On the Structure of the 
XI. Root. 
In the plant investigated the roots produced were all of 
one kind, and similar in structure to the earth-roots of A . evecta 
described by Russow. Transverse sections were cut of twenty- 
five roots taken at random from the plant, and in these the 
number of protoxylem-groups varied from ten to thirteen; 
further, the xylem elements were lignified to the centre of the 
root. The small number of protoxylem-groups and the total 
lignification of the xylem is described by Russow for earth- 
roots ; besides these, however, he mentions large air-roots, 
in which from eighteen to twenty protoxylem-groups were 
present, and in which only the outermost elements of the 
xylem were lignified. These air-roots appear to be absent 
in the particular variety of A. evecta under examination, but 
investigation into the structure of the large aerial roots has 
been carried out on material from the Cambridge Botanic 
Garden. 
After their entry into the ground the large roots branch 
frequently, more than one side-root being given off at times 
from the same level. The branch-roots bear no definite 
relation to the protoxylem-groups in the main root; thus the 
vascular tissue in the branch may be in connexion with one, 
two, three or more protoxylem-groups in the mother-root 
(Fig. 27). 
The structure of the earth-roots has been given in detail 
by Harting and by Mettenius, hence it will be only necessary 
here to allude to one or two points. 
Figs. 22 and 24 show the difference in structure between 
an earth- and an air-root. The endodermis is well marked in 
both, though it does not appear very clearly in the photo¬ 
graphs, but its structure is better seen in Fig. 20, which is 
a drawing of a well-preserved root obtained from the 
Cambridge Botanic Garden. In a longitudinal section of 
the root the walls of the endodermal cells appear waved, 
this being due to the occurrence of alternate bars and pits 
