May 1904] 
Element ory Mycology 
145 
cell — a tubular structure (so far as the wall is concerned) with 
one continuous cavity. In other cases cross partitions are devel- 
Fig. 5. Grape Mildew (Plasmopara viticola). A section of a grape leaf is 
shown between the cells of which the hyphae ramify and from which they draw nour¬ 
ishment. The hyphae emerge from a stomate in the lower surface to bear abundant 
conidial spores; these produce swarm-spores which grow into new plants. The 
two organs (oogonium and antheridium, Oog. & An.) are shown to the right above 
which produce the sexual spore ( Oospore , Oosp.). 
oped at closer or more distant points, and these septa divide the 
cavity into separate compartments; we then say the hypha is 
multi-cellular. The increase in the size of the cells in fungi and 
in other plants and their repeated multiplication, may result in the 
formation of tissue of lesser or greater extent, ultimately of sim¬ 
pler or more complex structure, and possibly manifold functions; 
also marked division of labor may ensue. 
Cell Multiplication. — Unicellular organisms (plants and 
animals) grow only by increase in size of the single cell — a di¬ 
vision (as in the multicellular forms) into two, these again divid¬ 
ing and so on, never taking place; however, it must be remem¬ 
bered that multiplication of individuals occurs — so-called fission, 
i. e., division into two equal parts. Such unicellular individuals, 
while extremely numerous, comprise only a small fraction of the 
total number of species in the organic world. They are small forms, 
