306 Bower . — The comparative examination of the 
either one end or the other. More especially is it desirable 
that such series should be as strictly defined as possible in 
those parts of the organic system which obviously lead as con- 
necting links from the lower to the higher, and in no part of 
the vegetable kingdom is such definition more necessary than 
in the Vascular Cryptogams. These are admitted to be a 
transition series from the simpler forms of Algal-Bryophytic 
affinity to the Phanerogams. It is now generally accepted 
that there have been at least three series of the Vascular 
Cryptogams, which after their first origin developed indepen- 
dently of one another : viz. the Lycopodineae, the Equisetineae, 
and the Filicineae ; the more clearly we are able to parcel 
out the members of these series according to their true affin- 
ities among themselves, the less complex will the problem 
become of recognising the relations of the series one to another, 
and their connection severally with the forms lower or higher 
in the main series of plants. 
It is reflections such as these which have led me from time 
to time to devote attention to the Filicineous series of Vascular 
Cryptogams, and it is the object of the present pages to give 
a general account of the characters of the meristematic tissues 
of root, stem, leaf, and sporangium in a number of these plants. 
Many facts regarding them are already well known, and these, 
together with freshly acquired facts, will be found sufficient to 
demonstrate that even in a character so apparently special as 
the structure of the meristematic tissues, these plants form a 
natural series. 
The distinction between eusporangiate and leptosporangiate 
forms, according as the sporangium is derived from a single 
cell or from a group of cells, was first emphasised by Goebel ] , 
and it has been generally adopted. It will be shown, 
however, and Goebel himself contemplates this as pos- 
sible 2 , that this distinction cuts in two what is obviously a 
natural and continuous series : that though it is useful to 
recognise the difference between plants in which the sporan- 
Bot. Zeit. 1 88 1, p. 717. 
2 Schenk’s Handbuch, III, p. 387. 
