134 THEORY OF THE STROBILUS 
independently in quite a number of series,”! and has shown that they must 
have been produced in different ways. Here then is polyphyleticism in 
high degree, seen in the origin of those parts of the gametophyte which on 
grounds of descent we have already separated from the foliar appendages 
of the sporophyte. 
Such results as these for the gametophyte lead us to enquire how the 
case stands as to the origin of foliar differentiation in Vascular Plants. 
In discussing such questions, it is to be remembered that in different stocks 
the foliar condition of the sporophyte as we see it may have been achieved 
in different ways, just as investigators have found reason to believe that it 
was in the gametophyte. We have no right to assume that the leaf was 
formed once for all in the descent of the sporophyte. But at the moment 
we are unprovided with any definite proof how it occurred. All the evidence 
on the point is necessarily indirect, since no intermediate types are known 
between foliar and non-foliar sporophytes. Physiological experiment has 
as yet nothing to say on the subject. The fossil history of the origin of 
the foliar state in the neutral generation is lost, for the foliar character 
antedated the earliest known fossil-sporophytes. There remain the facts 
of development of the individual, and comparison, while anatomical detail 
may have some bearing also on the question; but all of these, as indirect 
lines of evidence, fall short of demonstration, and accordingly it is impossible 
to come at present to any decision on the point. For the purposes of 
this discussion, however, we shall proceed on the supposition that all leaves 
of the sporophyte generation originated in essentially the same way, though 
not necessarily along the same phyletic line. 
There are at least three alternatives which may possibly have been 
effective in the origin of a foliar differentiation of the shoot, in any pro- 
gressive line of evolution of vascular sporophytes: (1) That the prototype 
of the leaf was of prior existehce, the axis being a part which gradually 
asserted itself as a basis for the insertion of those appendages; the leaf in 
such a case would be from the first the predominant part in the con- 
struction of the shoot. (2) That the axis and leaf are the result of 
differentiation of an indifferent branch-system, of which the limbs were 
originally all alike; in this case neither leaf nor axis would predominate 
from the first. (3) That the axis pre-existed, and the foliar appendages 
arose as outgrowths upon it; in this case the axis would be from the first 
the predominant part. 
The first of the above alternatives, viz. that the prototype of the leaf 
existed from the first, and was indeed the predominant part in the initial 
composition of the shoot, has been held by certain writers as the basis of 
origin of the leafy shoot in vascular plants.2. On this view not only is the 
1 Organography, p. 261. 
* Goethe, ‘‘Die Metamorphose der Pflanzen.” Gaudichaud, fem. de 1’ Acad. ad. Sci., 
1841. Kienitz Gerloff, Bot. Zect., 1875, p. 55. Celakovsky, ‘* Unters. ueber die Homo- 
logien,” Pringsh. Jahrb., xiv., p. 321, 1884; Bot. Zett., 1901, Heft. v., VI. 
