Lee. — Observations on the 
306 
bundles at a higher level. The second fact, which is really only an accentua- 
tion of the first, is that the extreme lateral bundles on either side invariably 
unite with the midrib at the apex of the cotyledon. 
To describe this in the reverse way. The first sections at the apex of 
the seed-leaf show no vascular bundles. Then, in the general case, a broad 
strand of vascular tissue arises. At first it is indefinite in outline, but lower 
down it separates into three distinct bundles, one being the midrib, the 
other two following the outline of the cotyledon and giving rise to the 
laterals. In the majority of cases, as we pass down the seed-leaf all the 
bundles branch, but the branches produced always fuse with one or other 
of the chief bundles before the base is reached, only the midrib and the 
two laterals persisting. The two exceptions to this are seen in III and v : 
in the former case four laterals (in addition to the midrib) persist, while 
in V all the laterals produced unite with the midrib before the latter enters 
the hypocotyl. 
The importance of this peculiar venation in connexion with the tran- 
sition cannot easily be over-estimated. This subject will be referred to 
again after the seedling anatomy has been described in more detail. 
Description of Species. 
The vascular anatomy of most of the species examined will now be 
described. 
A. Tubuliflorae. 
Tribe III, Astereae. 
Solidago ulmifolia , Muhl. Seedlings small (3-7 cm. long), each with 
two equal cotyledons, which are united along one side for a long distance 
before fusion occurs on the other margin. 
Seedlings A and B. Near the base of each seed-leaf there are three 
vascular strands, of which the two laterals are very small (Diagram 2, I). 
On the other side, where the cotyledons first unite, the lateral from one 
cotyledon fuses with its fellow from the other (Diagram 2, 11), and almost 
immediately the fused bundle, moving round in a clockwise manner (as seen 
from above), unites with one of the midrib bundles. On the other side, 
fusion of the laterals is followed by the passage of the double strand into 
the centre of the hypocotyl, where it remains quite distinct for some 
distance (Diagram 2, III and IV), finally moving slightly clockwise to join 
one of the xylem-strands in the cotyledonary plane. In the meantime, the 
midrib of each cotyledon has passed nearly to the centre of the hypocotyl ; 
the xylem in each case proceeds to undergo rearrangement, and the phloem 
group bifurcates. A transverse section at this level shows three xylem- 
masses, of which the intercotyledonary strand near the centre gradually 
