684 CONCLUSION 
in Phylloglossum; but in Lycopodium, Selaginella and Jsoetes there is 
dichotomous branching, often with unequal development of the shanks. 
Ophioglossum also shows dichotomy of the roots. But in Zgudsetum and 
in Ferns the branching is definitely monopodial, the lateral roots originating 
apart from the apex of the main root; a condition comparable with the 
origin of the lateral buds in Aguzsetum, or of the axillary buds in the Hymeno- 
phyllaceae. The similarity of these conditions to what is seen in axis and 
leaf is unmistakable. 
It is thus seen that in the axis, leaf, and root provision is made for 
amplification of each several part by branching, and the methods of 
branching seen in them all are essentially alike: each type of part may 
remain unbranched, or it may dichotomise, or show monopodial branching : 
it is also seen that dichotomous branching is prevalent in those forms which 
comparison or palaeontological evidence shows to have been primitive. It 
is natural that such analogies should exist between parts of the same 
individual plant; but there is no reason to see in them anything more 
than parallel modes of amplification of parts which were throughout their 
descent distinct in their origin, and in their nature.! 
An analysis of even the most complex types of the vegetative system 
in Vascular Plants involves only the factors thus disclosed, viz. the shoot 
consisting of axis and leaves, with occasional emergences and _ hairs, and 
the accessory roots. The apical growth of the shoot may be continued 
indefinitely, with indefinite repetition of its several appendages ; or it may 
itself be duplicated either by terminal or by lateral branchings, with or 
without accessory roots. In fact, the whole vegetative system of the plant- 
body, however complex, is built upon the simple shoot as the unit: its 
apex, initiated in the first definition of polarity in the embryo, shows 
continued apical growth with formation of an indefinite succession of 
appendages: it may fork at its distal end: or new shoots may be initiated 
below the apex: but still the whole plant-body is derived from the 
extension or it may be the forking or repetition of that fundamental 
unit—the shoot. 
1The fact that these structural analogies exist cannot rightly be held to show any 
common origin of those parts, unless examples of dichotomy can be brought forward in 
which one limb develops as one type of part, the other as another type; or unless a gradual 
transition from dichotomy to monopodial branching, such as is seen in the branching of the 
leaves of Ferns, smooths over the transition from branchings which produce parts of the 
same category to those which produce those of different category. Such direct evidence can 
easily be found indicating a common origin of rachis and pinna in the leaves of Ferns; but 
it has never yet been produced in support of the views of Potonié or of Tansley as to the 
common origin of axis and leaf, already alluded to above (pp. 628, 630). All the evidence 
adduced by them is indirect ; though the structural analogies are interesting, they carry little 
weight against the positive fact that in all observed cases the leaf originates normally as a 
lateral appendage of the axis. 
