RUELLIA AND DIANTHERA: AN ANATOMICAL STUDY 
THEO. HOLM 
(WITH TWO PLATES AND THREE FIGURES) 
Many genera of Acanthaceae have been studied from an anatomi- 
cal point of view, and the literature is quite extensive. Much atten- 
tion has been given, for instance, to the occurrence of the peculiar 
cystoliths, which seem to be especially characteristic of this family; 
the hairs, which are somewhat variable, have been studied also in a 
number of genera; and the several cases of anomalous stem-structure 
have attracted much attention. Suggestions as to an anatomical 
characterization of the family have been made by VESQUE," but only 
in connection with the leaves. The anatomy of several Ruellieae has 
been described by OLGA TcHoupRoFF,? and quite a comprehensive 
anatomical monograph of Thunbergia has been presented by RovULET.° 
With the exception of these works, no others dealing with a general 
treatment of the family have appeared. Therefore, in spite of the 
rather copious literature, one does not find more than a few scattered 
notes on the stem structure in general, relatively very little about the 
leaf, and almost nothing about the roots. It must be remembered, 
however, that the authors, as a rule, had to depend on herbarium 
material or specimens cultivated in botanical gardens. 
One species of Ruellia and one of Dianthera are very frequent in 
the vicinity of Washington, and since these species have not been 
examined so far, I studied them and found various points that may 
be of interest to students of plant anatomy. It will be seen from 
this study that Ruellia has a monostelic structure, which is typical 
of the stem of dicotyledons; while Dianthera has a polystelic axis. 
I was very much surprised in finding such structure in a member of 
t Caractéres des ep eee familles gamopétales tirés de l’anatomie de la feuille. 
Ann. Sci. Nat. Bot. 26. 
2 Quelques notes sur l’anatomie systématique des Acanthacées. Bull. Herb. 
Boissier 32550. 1895. 
3 Recherches sur l’anatomie comparée du genre Thunbergia L. fil. Bull. Herb. 
Boissier 23259. 1894. 
Botanical Gazette, vol. 43} [308 
