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 pinnae, 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 fiat 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 the Hartstongue (Scol. v. densum Kelwayii) and in the 

 Lady Fern (A. f. f. unco-glomeratum and A. /. /. 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 



