BULLETIN OF THE BUSSEY INSTITUTION. 329 
groundsel, the odspores of Peronospora gangliformis are produced. 
These are small globular bodies, with a thicker outer covering than the 
asexual spores have. ‘They are produced in the following way: The 
mycelium swells up into a sac or odgonium, which is cut off from the 
rest of the mycelium by a cross partition, shown in Fig. 4, 0; and the 
protoplasmic mass, s, rolls itself up into a ball at the centre, which is 
to become the spore. The antheridium, or male organ, is formed by a 
similar swelling at the end of another filament, which applies itself to 
the surface of the odgonium as shown at Fig. 4,a. The sexual act 
consists in the growth of a small tube, called the pollinoaium, from 
its supposed resemblance to a pollen tube, which penetrates to the 
protoplasmic mass in the centre of the odgonium. As a result of 
this contact, a wall of cellulose is formed around the mass which 
grows into the spore. These sexual spores, buried in the leaf, are 
Fic..5. Fig. 4. 
much tougher than the asexual, and can endure the cold of winter 
and drought of summer to a much greater degree. When the lettuce 
leaf dies, the proper leaf cells decay, leaving the odspores behind, 
which then, after the lapse of some weeks, begin to germinate. 
Another familiar case of a fungus having both sexual and asexual 
spores is seen in the Cystopus candidus or white mould on cruciferous 
plants, mustard, radishes, cabbages, &c. The asexual spores are here 
again on the surface of the leaf or stem, while the sexual are buried 
in the tissue. The former are not single as in Peronospora infestans 
and gangliformis, but in rows packed closely together, which, to the 
naked eye, appear like white spots on the leaves and stems. The 
odspores are produced in the same manner as those of Peronospora 
gangliformis, and differ from them in having certain brown wavy 
ridges running over them, as in Fig. 5. These odspores are only set 
free by the decaying of the leaf substance around them, and take a very 
vaL. I. 49 
