Evolution of Branching in the Filicales. 11 
ourselves what are the conditions necessary to ensure the 
production of a branch fundamentally similar in structure to the 
original axis. Evidently a fundamental similarity of growth- 
conditions for the two resulting growing points is the essential 
provision; granted this the two growing points will inevitably 
produce two essentially similar (dictyostelic) branches, and accord¬ 
ing to the degree of similarity in the growth conditions the form of 
branching will more or less closely resemble a dichotomy. However, 
when the conditions are fairly unequal the resulting branches may 
no longer be to one another as the two arms of a fork. One of the 
arms may “ tend to push the other aside and approximate to a 
continuation of the original axis.” 1 In time the one comes to be 
known as the “main axis” “giving off” the other as a branch, 
though both may in their vascular structure be dictyostelic. The 
dichotomy may pass insensibly into the monopodial type of branching. 
We have only to go a few steps further to arrive at the other 
extreme of our series, Fig. 1, F. It is a common occurrence for 
one of the products of division of the growing apex to become 
dormant almost immediately after its formation, while the other 
continues its growth as the main apex of the plant. This state of 
affairs is undoubtedly more specialized than, and easily derived 
from, that in which the two apices continue to grow side by side 
both utilizing to about the same degree the conducting system in 
their rear. One of the apices has been sacrificed to the better 
nourishment of the other, by passing over into a state of temporary 
inertia, and provision is thereby also made for a resumption of 
activity in case the main apex meets with an accident or otherwise 
becomes checked in its growth. 2 
1 Tansley, “ Lectures on the Evolution of the Filicinean Vascular 
System,” New Phytologist, 1907, p. 29. 
1 Such dormant buds, which trace their origin to the growing point, have 
to be distinguished from so-called adventitious buds, which appear in no 
constant position and as the result of a secondary meristematic activity in 
tissues already more or less mature. The former may conveniently be termed 
c< primary ” buds in contrast to the adventitious or 11 secondary ” buds. The 
ultimate distinction, however, is only developmental, and even that criterion 
would be difficult to apply in the case of adventitious buds arising near enough 
to the growing point, but the latter condition appears not to have been recorded. 
According to Sadebeck’s observations (Schenk’s Handbuch I, 1881, p. 266) the 
adventitious buds in Ferns appear to be confined to the leaves. Sadebeck 
mentions as an exception to this statement the buds in the Ophioglossaceae. 
Professor Lang, however, concludes from his detailed researches that the 
buds on the stem, at least, of Botyychium Lunaria and Helminthostachys are “ part 
of the primary construction of the plant,” and not adventitious as Farmer and 
Freeman (Annals of Botany, 1899, Vol. XIII, p. 423) had previously stated. 
From several other sources similar conclusions have come to light 
regarding the buds found in relation to the branching of Ferns. Thus, 
Hofmeister’s view (Beitriige etc. II, Abhandlungen der Kgl. Sachs. Ges. der 
