/ NTROD UCTIOA r . 
V 
formed above the root-stock do not move ; the third from the ground revolves, but at first very 
slowly. This species is a slow revolver : but Lygodium scandens made five revolutions, each at the 
average rate of 5I1. 45m. ; and this represents fairly well the usual rate, taking quick and slow movers, 
amongst flowering plants. The movement is in the usual direction — namely, in opposition to 
the course of the sun ; and when the stem twines round a thin stick it becomes twisted on its 
own axis in the same direction. In Gleichenia and other tropical ferns the rachis is dichotomous, 
or forked. When, as in the Hart’s-tongue, the frond is undivided, the rachis forms its mid-rib: 
but more usually the frond is more or less broken up into separate portions, and as in describing 
ferns it is necessary to use some terms expressing the nature of such division, we must here 
explain them. If the division does not extend down to the rachis, the frond still remains in a 
single piece, and the term segment is applied to the lobes, the frond being said to be pinnatifid 
or pinnatiscct ; and should these lobes be again partially cut into segments, the frond is called 
bipinnatifid or bipinnatisect. More generally, the division is more complete, and the frond is 
separated down to the rachis : the separate portions are then termed pinnce , and the frond said to 
be pinnate ; each pinna may be divided again into segments (pinnatisect), or cut into separate 
pinnules — when the frond is bipinnate. A further division results in a tripinnate fern, where the 
pinnules are divided into tertiary divisions. It is rare for fronds to be more compound than 
this, but the ultimate divisions are always described, and may be lobed, or toothed, or quite entire. 
Another important point to be observed is the venation , or the arrangement of the little 
veins or nerves which run in the substance of the frond. These are easily observed, and will be 
found very varied in character. Of course the simplest form is that where a single vein ( mid-rib 
or costa) runs down the centre of the segments, and this is seen in the filmy Hymenophyllece. 
More frequently there are secondary veins (veinlets) coming off in a pinnate manner from the 
central one, and running parallel to one another to the edge, or these may be forked, the 
branches proceeding to the margin, and ending before they reach it. This latter is a very common 
form, and may be seen in the Male Fern and the Bracken. Another type is found in the Maiden- 
hair, where there is no mid-rib, but the veins radiate in a fan-like way from the 
base. All these are cases of free venation, the separate veins, even when 
branched, never uniting again ; but there are numerous cases of anastomosing 
venation, where the branches of separate veins unite with one another to form 
a network of various kinds. Mr. John Smith, of Kew, Mr. T. Moore, of 
Chelsea, and other writers on Ferns, have very carefully observed these differ- 
ences, and have reduced the kinds of anastomosing venation to about seven 
different types. These it is not necessary to define here, as they are not 
represented in the European species to any extent. IVoodwardia, however, affords a good 
example of one of the forms of anastomosing venation, in which the veinlets are connected by 
little arched veins, and form thus many small spaces or areolce. 
By some writers a decided difference in venation is considered sufficient to make separate 
genera of ferns, whilst others pay little attention to this, and include in the large genera, such 
as Polypodium and Acrostichum, plants showing all the above varieties. It is this difference of 
treatment which causes the very great diversity in the estimate of the number of fern genera, 
and is one great reason of the numerous names (synonyms) which so embarrass the student. 
The growth of the fronds of ferns is very slow, much more so than that of the leaves of 
flowering plants. It takes two years to form a frond of the Male Fern, and others are probably 
longer in course of evolution before they commence to expand. When first noticeable they are 
closely curled up, the whole frond being rolled in on itself from sides and top, and forming a 
b 2 
PINNA OF MAIDEN- 
HAIR. 
