Notes . 
473 
of the plumular bundles, and the same applies to their metaxylem elements. A triarch 
root was thus formed. 
Pinus montana var. gallica, P. sy Ives iris, P. Thunbergii, P. Gerardiana, and 
others all follow a course similar to the above. There is, however, much variation 
both in the number of the seed-leaves and also in the behaviour of the bundles of the 
cotyledons. 
Tsuga diversifolia may be placed in a position intermediate between the Taxus 
and Pinus types. 
Conclusions. 
i . A mesarch structure is exhibited in the cotyledonary bundles of Cephalolaxus, 
Taxus, and possibly other plants. 
2. The Gymnosperms, as a whole, conform to Van Tieghem’s type 3 of rotation ; 
there are, however, three varieties of this type : (1), that in which the bundle of the 
cotyledon is endarch throughout, and the rotation of the protoxylem very indefinite, 
e.g. Cephalotaxus ; (2), that in which the seed-leaf-trace is endarch but the rotation 
of the protoxylem takes place in the hypocotyl, e.g. Cedrus ; and (3), that in which 
the rotation of xylem and bifurcation of the phloem of the cotyledonary bundle take 
place in the seed-leaf, e.g. Pinus. 
These varieties merge one into the other ; it is not possible to draw a definite 
line of demarcation between them. 
3. The numerous cotyledons obtaining in many plants have been formed by the 
splitting of pre-existing ones. This conclusion is based on the results obtained from 
the study of many individuals of species with a varying number of seed-leaves. 
T. G. HILL and E. de FRAINE. 
ON THE SEEDLING STRUCTURE OF CERTAIN CENTROSPERMAE \ — 
Nyctaginaceae : Allionia albida, Walt. — The petiole of each cotyledon contains 
a central strand, consisting only of a very few tracheae, derived from one of the 
bundles of the midrib, and bounded on each side by two normal collateral bundles, 
the smaller ones being outermost. Near the base of the^petiole the traces a fuse with 
the larger bundles b. The axis, at the level of the cotyledonary node, contains six 
plumular strands, which soon fuse together to form two. On the arrival of the seed- 
leaf bundles into the central cylinder, the groups of tracheae c 1 and c 2 occupy their 
isolated positions between the bundles b 1 , b 2, and b 3, b 4 respectively ; while b 2, 
b 4, and b 1 , b 3 are separated by the plumular traces d 2 and d 1 respectively. 
Following the hypocotyl downwards, the relations between the bundles are some- 
what complicated, c 1 and c 2 occupy their position throughout, but there is much 
anastomosing between the bundles of the series b and d. At the same time the 
protoxylem s of b 2, b 4, and b 1, b 3 rotate towards d 2 and d 1 respectively. This 
rotation is, however, vacillating, and the rearrangement arrived at may be obliterated 
1 Abstract of paper read before Section K at the York meeting of the British Association, 
August, T906. 
