THE FERN WORLD OF AUSTRALIA. 
3 
forms of venation may occm-, having the apices of the veins of 
either the first, second or third series combined in some way or 
other, thus if the whole system of venation is uniformly combined, 
so as to form a network, it is said to be reticulated ; if the simple or 
forked veins are united l3y a continuous vein parallel with or close 
to the margin it is said to be transverse marginal. Sometimes the 
apices of the venules of one series or fascicle combine with the apices 
of the adjoining series, this is called anastomosing ; of this arrange- 
ment there are some modifications as angular and arcuate or 
arched anastomosing, which are further modified by producing from 
their exterior side other outwardly-directed excurrent veins or veinlets, 
which are either free, terminating in the areoles (meshes) or margin, 
or anastomose- with the next superior venule. In some forms of 
netted venation, the venules are irregularly combined, the areoles 
or meshes producing from their sides certain simple or forked 
variously-directed veinlets, which terminate- within the unequal- 
sided meshes, this arrangement is called compound anastomosing. 
When the veins are somewhat elevated above the fronds surface 
they are said to be external, and when indistinct from their 
immersion in the fronds substance internal. 
From some part of the venation the fructification is produced, 
where this occurs the part will become thickened, this part is called 
the receptacle, and if situated at the apex of the vein or venule is 
said to-be terminal, between the base and apex medial, if seated on, 
the angular crossing, or point of confluence of two or more venules 
or veinlets, compital. 
It consists, in most cases of one-celled spore-cases, sporangia, or 
seed cases, more or less completely girt by an elastic ring, but in 
some cases of sporangia which are many-celled or destitute of the 
ring. 
These Spore-cases are mostly collected into masses which usually 
consist of multitudes of crowded spore-cases and is called a sorus, 
but being usually spoken of collectively the plural term sori will be 
more frequently met with ; these sori are either round or elongated, 
but sometimes they are of no determinable form when they are 
called am.oriihous. In most cases they are dorsal on the back of 
the frond, but sometimes they are marginal, or extra-marginal. 
The elongated sori are oblong, linear or continuous, and either form 
an angle with the midrib when they are said to be ohlique, or run 
parallel with the margin or midrib. In some groups of ferns the 
sori are entirely exposed on the surface of the frond, while others 
have the sori covered more or less by a thin skin called indusium or 
involucre of which there are various modifications — as cupshaped, 
vaulted, &c., &c. The foregoing remarks on the structure of a fern 
will be found in accordance with the views of most writers on the 
subject, and will assist the student not only to better understand 
this work but any other on the same subject. 
