324 BULLETIN OF THE BUSSEY INSTITUTION. 
see a filament which is just making its way through a breathing-pore, 
and, in the centre, an older one, which will be described presently. 
Within the leaf the mycelium is seen branching amongst the cells. 
Once in the air, free from the tissue of the leaf, the mycelium bears the 
reproductive bodies or spores,*——the term generally given to all bodies 
in the lower plants which take the place of seeds in the higher plants, 
by which the fungus, or, what is the same thing in this case, the disease 
is conveyed to other plants. The threads either grow straight forward 
or branch, and, at the tip or tips, swell until they attain the shape 
shown in Fig. 1, 6. They are cut off from the rest of the mycelium 
by a cross partition, and, when ripe, easily fall from their attachments. 
It must be noticed that these spores are asexual; that is, produced 
directly from the mycelial threads without the intervention of any 
sexual organs, such as are known by the names of antheridia and 
odgonia, terms which imply a functional resemblance to the anthers 
and ovaries of higher plants. Generally, just before the spore has 
fallen from the tip, the mycelium immediately below grows out on one 
side upwards, and again bears a spore at its end. In this way, the first 
spore is pushed over, so that, if it has not already fallen off, — which 
it is very likely to have done,—it looks as though it had grown from 
the side instead of the tip; and spore number two, which is really 
lateral, appears terminal. The nodes on the mycelium, represented 
in Fig. 1, c, show where previously formed spores have dropped off, the 
first having been the lowest down. 
* The term spore applied to fungi is extremely vague, since it denotes all the 
reproductive bodies, without_regard to their origin or structure. The most 
natural division of spores seems to be that of many continental mycologists into 
odspores, or those produced by some sexual action, and asexual spores. The 
term sporidium does not seem to me to be advisable, inasmuch as it denotes 
bodies of quite different origin; for example, in Mucor the so-called sporidia 
are asexual, while in the Perisporiacez the asci are products of a growth follow- 
ing a sexual action. The immense variety of asexual spores in fungi prevents 
us from using a single word which will apply equally well to all cases. The 
term conidia is now quite generally adopted to express collectively the asexual 
spores. The body containing spores is known as a sporangium. In the case of 
Peronospora infestans, we are at a loss to know what term to apply to the aerial 
fruit shown in Fig. 1,5. If the germination always took place as in Fig. 2, b, 
we should have no hesitation in calling the body a spore. If it always ger- 
minated by zodspores, as in Fig. 2, c, we should call it a sporangium or zo- 
osporangium. The question is merely a vérbal one, however. ‘The facts in the 
case are easily understood. 
