Tissues in Certain Monocotyledons. 45 
We are not aware that the anatomy of the stem in any of 
these species has so far been described. Professor F. O. 
Bower, F.R.S., first called our attention to the occurrence of 
secondary growth in thickness in Arts tea corymbosa , and to 
him we are also indebted for the supply of abundant fresh 
material from the Glasgow Botanic Garden. 
Arts tea corymbosa is a low shrub ; the stems are elongated, 
much branched, and cylindrical ; the younger branches are 
flattened in the plane of the distichous leaves, which are 
equitant, linear, rigid, and erecto-patent, attaining a length of 
from 4 to 6 inches 1 . 
It may be mentioned at once that the external characters 
of the other three shrubby Irideae are very similar to that of 
our species. Aristea fruticosa , Pers., is a dwarf under-shrub, 
much smaller in all its parts than A. corymbosa. Witsenia 
maura , Thunb., on the other hand, is a tall plant, with woody 
erect stems 2-4 feet long; Klattia partita , Baker, is perhaps 
the most like Aristea corymbosa in appearance ; its woody, 
branched stems are 1-2 feet in length. All four species 
agree in their distichous equitant leaves, and flattened 
branches which become cylindrical with advancing age. It 
is highly probable that the account of the anatomical struc- 
ture and development which we are about to give in the case 
of A. corymbosa will be found to hold good in essentials for all 
these shrubby forms. 
1. Primary Structure. — We will begin with a short descrip- 
tion of the primary structure. 
The equitant leaves are in their upper ensiform portion 
typically centric in structure, with assimilating tissue and 
stomata on both sides. The collateral vascular bundles form 
a flattened ring, the xylem in each facing towards the interior, 
synonyms will be found ; also Baker, Systema Iridacearum, Linn. Soc. Journal, 
Bot., vol. xvi. 1878, pp. 108-110; Bentham and Hooker, Genera Plantarum, 
vol. iii. 1883, pp. 701, 702. 
1 The above is a slight extension of Baker’s description, Handbook of Irideae, 
P- *45- 
