TYPES OF VARIATION 53 
not at the outset, multiplies itself, and forms as many independent 
tips which radiate, and may or may not divide again and again, 
but there is no cohesion, the tendency is always to grow apart. 
This tendency to multiply the terminal points extends, in some 
cases, to the fourth degree of subdivision; that is to say, the tip 
of the frond bears a tassel, the pinne, or primary side divisions, 
bear smaller ones, the pinnules, or secondary side divisions, do the 
like on a still smaller scale, and finally, the minute subdivisions of 
these, or pinnulets, are distinctly fanned, showing that the same 
tendency prevails throughout. Since, however, these tassels only 
occur at the tips, i.e. after a definite growth of the midribs primary, 
secondary, or tertiary, on single or normal lines, we have the singular 
fact that at a certain definite point of growth in many thousands of 
cases in such a subdivided plant, the midrib suddenly adopts a 
different plan of growth, and commences to split up and multiply 
itself to form a tassel. This tendency evinces itself in very varied 
ways. The terminals may divide on fan-like flat lines to form 
radiating points, these radiating points may divide again, or again 
and again, to form heavy pendulous flat tassels, or the division 
may occur on other radiating lines so as to produce bunches, also 
of single points or multiplied ones, so as to form corymbs or round 
masses. It is clear that many forms of tassel may result in this 
way, and hence the “ cristate " section is a large one. Allied to 
this are those Ferns which branch irregularly, their frond stalks 
commencing to branch near the base and doing so repeatedly, 
the leafy portion being carried by branching midribs, and only 
assuming the strap or leafy specific form if a sufficient cessation 
of the branching occurs. Such forms are in some cases associated 
with regular crests (see Appendix) with fine effect. In extreme 
cases of this type the whole Fern resembles a ball of moss, as is 
seen in Ше Hartstongue (Scol. v. densum Kelwayii) and in the 
Lady Fern (A. f. f. unco-glomeratum and A. f. f. acrocladon.) The 
second main section, in which the fronds are divided to a greater 
extent than the normal one (the opposite cases are too rare to be 
considered here), undoubtedly embraces a large number of the 
most beautiful forms existing. This type of variation would appear 
to depend very much, if not entirely, upon a primary simplicity 
of the vein system of the Fern concerned, the little veins which 
carry the cell tissue must be mostly free, that is, not forming a 
network, as we see in most flowering plants and many Ferns, 
but starting from the midrib, run out to the extreme edge of the 
frond, and to the points of the subdivisions. In such case, if they, 
by virtue of “sporting,” continue to grow beyond normal lines, 
they, as tissue-forming feeders, carry the tissue with them, following 
the specific tendency, and in this way, for instance, a Common 
Polypody (Polypodium vulgare) with normally smooth-edged 
pinnate divisions, but with free veins terminating at the smooth 

















