. Foundations of botany. om the surface of theliquid with a medium power of the microscope (half-inch objective)to see how the development of hyphae from the spores TYPES OF CRYPTOGAMS; THALLOPHYTES 259 After about twenty-four hours examine another portion of themould from the surface of the liquid and study the more fullydeveloped mycelium. Zygospores.—Besidesthe spores just studied, zygo-spores are formed by conju-gation of the hyphse of theblack moulds. It is not veryeasy to find these in processof formation, but the studentmay be able to gather fromFig. 190 the n
. Foundations of botany. om the surface of theliquid with a medium power of the microscope (half-inch objective)to see how the development of hyphae from the spores TYPES OF CRYPTOGAMS; THALLOPHYTES 259 After about twenty-four hours examine another portion of themould from the surface of the liquid and study the more fullydeveloped mycelium. Zygospores.—Besidesthe spores just studied, zygo-spores are formed by conju-gation of the hyphse of theblack moulds. It is not veryeasy to find these in processof formation, but the studentmay be able to gather fromFig. 190 the nature of theprocess by which they areformed,—a process which can-not fail to remind him of theconjugation of pond-scum. THE STUDY OF WHEAT RUST (PUCCINIA GRAMUN^IS) 310. Occurrence. —Wheatrust is common on cultivatedwheat and other grains, andalso on many wild and culti-vated forage grasses. In fact,this or similar rusts occur ona very large number of grasses,and many species of such rustsare recognized. A rust may. Fig. 190. — Formation of Zygospores in aMould {Mucor Mucedo). 1, threads in contact previous to conjuga-tion ; 2, cutting off of the conjugatingcells, a, from the threads, 6; 3, a laterstage of the process ; 4, ripe zygospore ; 5,germination of a zygospore and formationof a spore-case. (1-4 magnified 225 diam-have one, two, or three kinds * ^ ^^^^^^^ ^t,out 60 diameters.)of spores, and when three occur one is known as the cluster-cup stageand the others as red rust and hlack rust, according to the usualapproximate color of the spores. The rust called Puccinia graminisgrowing on wheat has its cluster-cup stage on the leaves of barberryin June. The spores from the cluster-cups are carried by the windto the wheat, where they germinate and in a few days produce the 260 FOUNDATIONS OF BOTANY red rust. A little later the black spores appear, produced from thesame mycelium.* This growth is chiefly upon the stems and sheaths.
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