Fungous diseases of plants . this ascogonium containsalways two nuclei, and these fuse prior to the development of thiscell as an ascus. This is the case when a single ascus is produced,and it is only slightly more complex when many asci result ( 85, d-f). Following the fusion of the two gametic nuclei,hyphal branches arise from the stalk cell of the oogonium. Theseconverge around the oogonium and finally completely incloseit. Within this first layer a second layer of hyphse is producedin similar manner; and subsequently, by outgrowths from each of 2 20 FUNGOUS DISEASES OF PLANTS 1 thes
Fungous diseases of plants . this ascogonium containsalways two nuclei, and these fuse prior to the development of thiscell as an ascus. This is the case when a single ascus is produced,and it is only slightly more complex when many asci result ( 85, d-f). Following the fusion of the two gametic nuclei,hyphal branches arise from the stalk cell of the oogonium. Theseconverge around the oogonium and finally completely incloseit. Within this first layer a second layer of hyphse is producedin similar manner; and subsequently, by outgrowths from each of 2 20 FUNGOUS DISEASES OF PLANTS 1 these layers into all available space, smaller hyphae are protruded;thus a compact inclosing body or perithecium is developed. Withthe further growth of the perithecium and the increase in sizeof the ascus, the inner layer and all internal hyphal branchesare dissolved and appropriated. Meanwhile, the outer layer be-comes yellow or brown and forms the true wall of the peri-thecium. From the wall cells of the perithecium there are. Fig. 86. Spore Forms and Appendages of ; a, ErysipJic Polygoni; l>, PodospJucra Oxyacauih(r ; c, Microsflurra Alni; c, PliyllncflniaCory lea; ^/and/, Ihuiuula ticcator produced, either from the base or from a more or less equatorialplane, the characteristic appendages. In a few cases only areappendages produced from the apex. At maturity there are oneor more asci, depending upon the genus, and each ascus con-tains normally from two to eight spores, the shape of the ascusvarying from practically spherical in the one-ascus forms toclavate or cylindrical where there are two or many asci. Thespores are one celled and colorless. As a rule the ascosporesdo not germinate immediately, requiring a period of rest. By ASCOMVCETES 221 the following spring the perithecia are very brittle and are saidto break open forcibly in water, after which time the ascosporesreadily germinate. The appendages of the perithecium are verydifferent in structure from the
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