716 CONCLUSION 
It thus appears that comparison of the several phyla, as represented 
both by their fossil and their modern representatives, leads “in each case 
‘towards the recognition of a primitive type, and that its construction tn 
the several phyla has certain features tn common. The chief of these 
are the definition of axial polarity in the first initiation of the embryo: 
the continued apical growth: the radial construction of the shoot: the 
origin of the appendages laterally from the axis by enation, and in strictly 
acropetal order: a protostelic structure of the conducting system of the 
axis, and a leaf-trace composed of a single strand, which comes off from 
the protostele with the minimum of disturbance of its structure. The 
appendages were from the first of two kinds which were closely associated 
together: bracts or leaves, and spore-producing members: the structure 
of these, and their relations to one another and to the axis, varied in 
the different phyla, and gave them their distinctive characters: but a, 
whorled arrangement of the bracts was prevalent in early small-leaved 
forms, while they commonly held a subtending relation to the spore- 
producing members. A body such as that sketched appears to have been 
common for all the early Pteridophytes, and constituted the primitive shoot. 
There is no clear indication, beyond comparison based on the facts of 
embryology and of mature structure, how such a body was in the first 
instance produced; but this leads to the hypothesis put forward in 
Chapter XI. The sporophyte, thus constituted, probably arose originally 
as a structure of limited size, and unbranched, upon a prothallus of 
considerable dimensions, and producing Homosporous Spores. From it, by 
branching of the axis, by differentiation of vegetative and propagative 
regions, by amplification of the leaves and spore-producing members, by 
adoption of an alternate leaf-arrangement as the leaves enlarged, and 
by expansion of the vascular system to meet these additional require- 
ments, all the known homosporous types may be understood to have 
originated. But as explained in Chapter XLVI, the adoption of 
Heterospory, and of the Seed-Hadit supervened later. This, while it has 
led to the final independence of the Land-Flora as regards external fluid 
water for the completion of its Life-Cycle, has brought as a secondary 
consequence a wide-spread reduction. 
The final goal of all organic development is the establishment of 
new individuals. The evolutionary story of the sporophyte illustrates this 
in two distinct ways. Jn the prior and non-specialised homosporous forms 
large numbers of germs are produced: those are individually small, and 
ill provided with nourishment, but they make up for deficiency of method 
by their large numbers. The larger their number the better the chance 
of survival and spread of the race: consequently amplification of the whole 
sporophyte is the leading characteristic of these earlier and simpler types; 
it was carried out either by multiplication of appendages individually small, 
as in the microphyllous types, or by enlargement of individual appendages, 
as in the megaphyllous types. It was in these homosporous forms that 
