130 FERNS. 
instances takes place laterally, marginally or peripherically, for 
which reason they are called Thallogene: Many Mushrooms how- 
ever produce stemlike organs, while again numerous Algz and 
Lichens form stems and branches and even (as in some Caulerpz) 
leaflike segments. Again some Hepaticee form thallus-like flat 
expansions, so far resembling rather Lichens though more deter- 
minate in form. Nevertheless all Thallogens are well separable 
from all Acrogens by the structures of their fruits ; but these are 
examinable only by the aid of a compound microscope and not 
‘ easily brought within the reach of exact scrutiny of tyros, for 
whom these pages are written, practical instructions for preparing 
the delicate microscopic objects being required. Still in collec- 
tions made by beginners, also these plants should not be neglected, 
so as to render the material available for study at any future time, 
and to make the young student at the very outset familiar with at 
least the external forms of these plants. Of Marsiliaceze we have 
well known examples in the Nardoo (Marsilea quadrifolia with 
many varieties), the foliage resembling that of a Clover with 
four leaflets ; further in the Azo//as (Azolla Magellanica and A. 
pinnata) which in large often purplish sheets float like duckweeds 
(Lemnas and Wolffias) on the surface of tranquil waters. Charas 
(and the closely allied Nitellas) grow submersed in water, and are 
easily recognised among plants of fresh or brackish water by their 
whorl-like branchlets, which resemble segments of foliage. 
By far the greatest number of Ferns belongs to the suborder or 
tribe of Polypodiaceee, as well here as elsewhere. The genera 
are mainly founded on the form and position of the fruitmasses 
and on the shape or absence of the involucre. Those represented 
in our colony, may be recognised by the following brief defini- 
tions, the explanation of fuller details being beyond the scope of 
this introductory book. 
I.—POoLYPODIACE. 
Dicksonia: Fruitmasses marginal, roundish. Involucre, bi- 
valved or cupshaped. Receptacle elevated. 
Cyathea: Fruitmasses dorsal, roundish. Involucre cupshaped. 
Receptacle elevated. 
