. Botany, an elementary text for schools. Botany. ^22. SimiiHcr-spores of willow mUdew. leaf and nourishes itself by sending short branches into the cells of the leaf to alDsorb food-materials from them. Numerous sitmmer-sporcs are formed on short erect branches all over the white surface. One of these branches is shown in Fig. 3212. When it has grown to a certain length, the upper part begins to segment or di- vide into spores which fall and are scat- tered by the wind. Those falling on other willows reproduce the fungus there. This process continues all summer, but in the later part of the s
. Botany, an elementary text for schools. Botany. ^22. SimiiHcr-spores of willow mUdew. leaf and nourishes itself by sending short branches into the cells of the leaf to alDsorb food-materials from them. Numerous sitmmer-sporcs are formed on short erect branches all over the white surface. One of these branches is shown in Fig. 3212. When it has grown to a certain length, the upper part begins to segment or di- vide into spores which fall and are scat- tered 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 pro- vision 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 peri- ihecia, shown in Fig. 32;L To the naked eye they appear as minute specks, but when seen under a magnification of 200 diameters tliey present a very interesting appear- ance. They are hollow sphoricnl bodies decoratt'd around the out- side with a fringe of crook-like hairs. The resting-spores of tiie willow miltlf'W are produced in sacs or asci inclosed within 1ht< leathery pcrithecia. Fig. ;!J4 shows a cross-section of a jieii- thecium witli the asci arising from tlie bottom. Tlio spores remain secuiely jiackeil in tiii' l)eritiieci!i. Tiicy do not ripen in the autumn but fall to the ground with tiie leiif and there remain 1 f<ili:ige. 'I'lie following spring. .'i2ri. I'lTitlii'i'iuiii of willow uiilil securely protected among tiie they mature and are liberated by tlie decay of the ])erithecia. They are tlien ready to attack the un- folding leaves of the willow and npeat tiie vork of the summer before. Wlicdt rust.—The development of some of the rusts, like tlio common wheat rust (I'uccinia gra- minis), is even more interesting and conipiicuted •'-I than tiiat of the mihh-ws. Wheat rust is also u |H-rit)i>'<'iiiiii cif wil- low
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Keywords: ., bookauthorbai, bookcentury1900, bookdecade1900, booksubjectbotany
