SEEDLING STRUCTURE IN THE LEGUMINOS. 53 
sativum, and a species of Lathyrus; while adding no new facts of importance 
he propounded a novel view of the nature of the medullary xylem in the 
epicotyl. Chauveaud (1911, p. 341) studied Lathyrus odoratus, paying much 
attention to the details of development of the vascular system, and also 
Ervum Lens and Vicia Faba. 
My own researches and a study of the literature have shown that, with 
very few exceptions, the seedling structure is very uniform throughout the 
Viciew, the chief differences being in relation to size. In the majority of 
cases, therefore, I have no new facts to record. A detailed description, 
however, will be given of the structure of Pisum sativum and Vicia Faba, in 
which species certain fresh points of interest have been observed ; and other 
species will be mentioned very briefly. 
Pisum sativum, Linn. (Pls. 1. fig. 10 ; 8. fig. 105 ; 9. figs. 98-104.) 
A tall herbaceous annual, climbing by leaf-tendrils. The hypocotyl is 
very short, the change of epidermis taking place a few mm. beneath the 
cotyledons. The cotyledons remain in the testa below ground ; they are 
inserted at less than a right angle from one another, and lie laterally to the 
direct course of the axis. The epicotyl bears two or three trifid bracts and 
then the foliage-leaves ; the arrangement of leaves is distichous and the 
stem is quadrangular. The main shoot has comparatively short internodes 
and usually dies after a time, the growth being continued by branches with 
longer internodes, which arise in the axils of the lowest braets or leaves. 
The diameter of the stem just above the ground is much less than in the 
upper internodes *. 
The root is triarch ; the xylem is made up of three long and massive 
radial plates of small elements, which do not extend to the centre, but are 
‘connected into a solid xylem star by larger metaxylem elements. There are 
three groups of strong fibres in the phloem, The endodermis is conspicuously 
dotted. 
As we pass up into the hypocotyl the xylem loses its regular appearance, 
the radial plates becoming loose groups with a mesarch development ; the 
central metaxylem begins to move outwards and parenchyma appears in its 
place. The three phloem bundles begin to divide, each separating into two 
groups. At the same time the two primary xylems destined to supply the 
cotyledons inerease their angular distance and begin to move outwards. 
Just below the cotyledons the xylem consists of two cotyledon traces and a 
first-leaf trace, all mesarch and similar in appearance ; and three tangential 
bands of metaxylem, which connect the cotyledon and leaf-traces and surround 
the fair-sized pith (Pl. 9, fig. 98). 
5 
* The small diameter of the base of the stem when compared with the size of the aerial 
system is strikingly shown in the fasciated monstrosity known as the Mummy Pea. 
