54 
MILDEWS, RUSTS AND SMUTS 
different kinds of reproductive organs met with as in the 
Uredinaceae, more especially in the genus Puccinia. 
At this point it may be well to explain the meaning of 
the word spore. A spore is the equivalent of a seed in 
flowering plants, inasmuch as it is capable of germinating 
and producing a new plant ; the seed of a flowering plant 
is furnished with an embryo or minute plantlet, whereas 
no such structure is present in the reproductive body of a 
fungus, hence it is not called a seed, but a spore ; in some 
instances the term spore is used when the reproductive 
body is asexual in origin, in fact the term, spore, is often 
used for every reproductive body produced by fungi. 
Pycnidia 
The first form connected with reproduction at the com¬ 
mencement of the cycle of development in some species, 
is called -a. pycnidium (pi. pycnidia). The same structure 
is in some books called a spermogonium (pi. spermogonia). 
Pycnidia are minute, flask-shaped structures when seen in 
section, and usually occur in clusters on discoloured spots 
on living leaves, etc., the open mouths of the flask-shaped 
pycnidia projecting above the surface of the leaf, for the 
purpose of allowing of the escape into the air of the minute 
bodies produced in the interior of the pycnidia, which are 
called spermatia or pycnospores. Pycnidia possess no 
functional value as reproductive organs at the present 
day ; the minute spermatia are supposed to represent the 
male fertilising element at some past period, when these 
fungi possessed a sexual mode of reproduction. 
Aecidia 
The first reproductive body of functional value at the 
present day is the aecidium (pi. aecidia). Aecidia usually 
appear early in the season, in more or less crowded clusters, 
on discoloured spots on living leaves or other parts of plants. 
The spores are produced in rows or chains, and consist 
of one cell, the oldest spore at the tip or apex of the chain 
becoming free at maturity, while young spores are produced 
at the bottom or base of the chain. In the most perfect 
forms of aecidia, numerous chains of spores are closely 
crowded side by side, and enclosed in a general envelope 
or peridium which is closed in the young stage, but becomes 
ruptured at maturity in a more or less stellate manner at the 
aqjex, the torn teeth usually bending outwards, and exposing 
the mass of orange or golden-yellow spores. Such structures 
are popularly known as " cluster-cups." The spores, 
