(Fig. 276). These patches consist of numerous interwoven threads that may be recognized under the microscope as the mycelium of the fungus. The mycelium in this case lives on the surface of the leaf and nourishes itself by sending short branches into the cells of the leaf to absorb food materials from them.
An image should appear at this position in the text. To use the entire page scan as a placeholder, edit this page and replace "{{missing image}}" with "{{raw image|First course in biology (IA firstcourseinbio00bailrich).pdf/223}}". Otherwise, if you are able to provide the image then please do so. For guidance, see Wikisource:Image guidelines and Help:Adding images. |
Fig. 276.—Colonies of Willow Mildew.
An image should appear at this position in the text. To use the entire page scan as a placeholder, edit this page and replace "{{missing image}}" with "{{raw image|First course in biology (IA firstcourseinbio00bailrich).pdf/223}}". Otherwise, if you are able to provide the image then please do so. For guidance, see Wikisource:Image guidelines and Help:Adding images. |
Fig. 277.—Summer-spores of Willow Mildew.
An image should appear at this position in the text. To use the entire page scan as a placeholder, edit this page and replace "{{missing image}}" with "{{raw image|First course in biology (IA firstcourseinbio00bailrich).pdf/223}}". Otherwise, if you are able to provide the image then please do so. For guidance, see Wikisource:Image guidelines and Help:Adding images. |
Fig. 278.—Perithecium of Willow Mildew.
An image should appear at this position in the text. To use the entire page scan as a placeholder, edit this page and replace "{{missing image}}" with "{{raw image|First course in biology (IA firstcourseinbio00bailrich).pdf/223}}". Otherwise, if you are able to provide the image then please do so. For guidance, see Wikisource:Image guidelines and Help:Adding images. |
Fig. 279.—Section through Perithecium of Willow Mildew.
Numerous summer-spores are formed of short, erect branches all
over the white surface. One of these branches is shown in Fig.
277. When it has grown to a certain
length, the upper part begins
to segment or divide into spores
which fall and are scattered by the
wind. Those falling on other willows
reproduce the fungus there.
This process continues all summer,
but in the later part of the season
provision is made to maintain the
mildew through the winter. If some
of the white patches are closely examined
in July or August, a number
of little black bodies will be seen among the threads. These little
bodies are called perithecia, shown in Fig. 278. To the naked eye
they appear as minute specks,
but when seen under a magnification
of 200 diameters they
present a very interesting appearance.
They are hollow spherical
bodies decorated around
the outside
with a fringe
of crook-like
hairs. The
resting-spores of the willow
mildew are
produced in
sacs or asci inclosed
within
the leathery
perithecia. Figure 279 shows a cross-section of a perithecium
with the asci arising from the bottom. The spores remain securely