Influence of the Adult Plant upon the Seedling. 325 
With regard to histological details the bundles have a general 
gymnospennous appearance, the xylem being composed of narrow 
tracheae, which shew but little variation in size ; the phloem, 
however, is fairly distinct (Fig. 5). The great point of resemblance 
is found in the presence of transfusion tracheides in Persoonici. 
Fig. 7. P- lanceolata.% Transverse section of a cotyledon cut just behind 
the apex, shewing the transfusion tracheides. x 280. 
These elements are found in greater or lesser abundance 
throughout the whole length of the cotyledon generally in proximity 
to the vascular bundle ; they extend almost to the apex of the seed- 
leaf (Figs. 6 and 7), further than the vascular bundle, where they 
may pass outwards from their central position to within one or two 
cells of the epidermis (Fig. 8). This lateral extension varies ; in 
some cases there may be a more or less continuous chain of trans- 
usion elements, as shewn in Fig. 8, or, in other cases, small 
groups of these cells may be scattered in the mesophyll towards the 
periphery. 
On passing downwards from the apex of a seed-leaf, the trans¬ 
fusion tracheides are seen to join, more or less completely, with the 
xylem of the vascular bundle ; and at this level, or just below, 
there is generally a diminution in their number, at any rate for 
a short distance. 
In the lower regions these particular cells are most marked on 
the flanks of the bundles, where as many as ten may form a con¬ 
spicuous group (Fig. 5)]: the number, as was to be expected, varies 
considerably in sections taken from different levels. 
The transfusion tracheides, however, are not restricted to the 
