138 BOTANICAL GAZETTE [FEBRUARY 
the writer to determine which shall be adopted by his readers. In 
some groups, as in the bacteria, species are perforce determined 
almost exclusively by physiological characters, while in other 
groups, as in the seed plants, morphology alone determines the 
matter. In the parasitic fungi various infection experiments have 
shown that numerous species which occur on several hosts may be 
composed of physiological races, each confined to its particular 
host. Such a treatment seems to the writer an entirely satisfactory 
manner of expressing the facts, and he does not see that there 
would be any gain in considering the forms specifically distinct. 
The development of the resting spores 
Although the resting spores do not appear in numbers until 
several generations of zoosporangia have matured and discharged, 
it will be more convenient to describe them before the more com- 
plex development of the zoosporangia is taken up. The very 
youngest resting spores seen measure about 70 in length (fig. 1). 
They consist of an elongated germ tube with an external button 
marking the position and size of the zoospore from which they 
originated. The distal end has already begun to enlarge, but the 
nuclei (5 #) are not much larger than those of the zoospores. The 
germ tubes do not seek out the stomata even when close beside 
them (fig. 11), but force their way between the epidermal cells 
at any point. After penetrating a variable distance, usually until 
a vascular bundle has been reached, the tube begins to swell up and 
gradually it acquires a globular form. The swelling out of the 
cyst is very much more rapid than the growth of the protoplast, 
which in consequence becomes highly vacuolate (fig. 2), like an old 
cell far back from the growing point in an ordinary plant. There 
is an attenuate peripheral layer of cytoplasm connected by radial 
strands with the central body surrounding the nucleus, which 
likewise has grown but little. At the very beginning of the enlarge- 
ment of the basal portion, the protoplast withdraws from the narrow 
neck of the germ tube, which is later cut off by a wall. 
Even when full sized, the parasite distorts the tissues of the host 
but very little. Most of the cells which lie adjacent to it appeat 
as though cut off to make room for its growth rather than crowded 
