178 AMONG THE WILD FLOWERS. 
stem sends forth its fronds sometimes in circular 
bunches, sometimes at intervals singly; in the 
Tree-ferns of warm climates the stem, in that 
case called a Ste, whilst continually producing 
circles of fronds at its summit, rises in course 
of time to the perpendicular height of 50 or 
60 feet. The stalk to which the leafy growth 
is attached is called the vachzs, sometimes the 
stipes, or stipe; the leafy part may be either 
entire, or more or less divided, frequently pin- 
natifid, the divisions in that case being pzzxe, 
wings; and if these pinne are again divided, as 
they often are, the sub-divisions are called 
pinnules. 
In any case the leafy portion of the frond is 
traversed by ribs and veins from which arise 
the little clusters of fructification called sovz, 
the plural of sovus,a cluster. These sori vary 
in different ferns both as to shape and contents 
and method of opening when the seed-dust, 
consisting of spores, is ripe. 
If the frond you have gathered is one of the 
gracefully arched fern Lastrea dilatata,a very 
common species, you will find underneath it 
rows of sori, regularly arranged, springing from 
the lateral veinlets of the pinnules. With a 
