26 i 
Facts relating to the Structure of Seedlings. 
elements takes place so as to bring about a root-like structure. Also, there 
is no structural hypocotyl ; the hypocotyl of these higher plants shows 
root-structure throughout except for a very short region below the cotyle- 
donary node, and the primary root-structure is diarch. Thus it is seen that 
with regard to the cotyledonary strands, the high transition and the 
consequent absence of a distinctive structural hypocotyl, certain Gymno- 
sperms, e. g. Cupressus ohtusa , Libocedrus , &c., and Angiosperms, e. g. 
Pup alia purpurea , Claytouia , &c., show marked Fern-like characters. 
The next stage in the series is represented in plants such as Phyto- 
lacca dioica , Lupinus venusta, Piper coruifolium , Pinus and many other 
Gymnosperms in which the seed-leaf-trace bifurcates either on its way 
through the cortex to the central part of the axis or in the cotyledons 
themselves, this bifurcation being accompanied by vascular rearrangements 
which are inaugurated at different levels. This, it may be pointed out, 
is paralleled in the fronds of certain Ferns ; in Angiopteris , for example, 
the first leaves have single leaf-traces, but in later formed leaves this single 
strand bifurcates at first at the periphery of the stem and then closer 
and closer to the central cylinder until two traces are given off from 
the cauline vascular strands instead of one. 
In the higher plants the extreme case of this early division of the 
cotyledonary strands results in the formation of two bundles, e. g. in Ephedra , 
Podocarpus, Araucaria , and Ginkgo , and in the Nyctaginaceae and other 
Angiosperms, which are together equivalent to the single strand of forms 
such as TaxuSy Juniperus, Cupressus, and Callitris amongst the Gymno- 
sperms, and Claytouia , Pupalia , and Ranuncidus amongst the Angiosperms. 
The final stage in complication is due to the lateral bundles ; these 
may fuse on to the single or on to the adjacent halves of the divided 
central strand, or, on the other hand, a series may be drawn, as in the 
Centrospermae , 1 in which the lateral bundles delay their fusion with the 
central strand more and more until, finally, they may occupy a prominent 
position within the hypocotyl, in the intercotyledonary plane, and give 
origin to two poles of the tetrarch root. In the extreme case the resulting 
root-structure will be tetrarch, e. g. Convolvulus siculus, but in less extreme 
instances the root-structure will be diarch throughout or tetrarch to begin 
with, becoming reduced to diarch, e. g. Scorzonera hispanica , Achillea 
Ptarmica , Tagetes patula , Coreopsis tinctoria , and Helianthus lenticulatus . 
So much for an alternative hypothesis which, in its broad lines, was 
originally held by Tansley . 2 3 From the purely morphological point of view 
it has, we think, as much to recommend it as the theory of Miss Thomas. 
To the latter investigator 3 c it appears easier to imagine the derivation 
1 Hill and de Fraine : Centrospermae, loc. cit. 
2 The Meeting of the British Association at York. New Phyt., vol. v, 1906, p. 184. 
3 Loc. cit. 
