. Hardwicke's science-gossip : an illustrated medium of interchange and gossip for students and lovers of nature . <:~ Fig. 148.—Leaf of Sycamore, with black ungus spots. FUNGUS SPOTS ON SYCAMORE LEAVES. IN answer to the inquiry that was made in one of thenumbers of Science-Gossip as to the cause ofthe spots on sycamore leaves, several have beenalready suggested. The most frequent cause of spotson the leaves of that tree is the fungus which Ipurpose to describe in this article. With the aid ofthe figures I have drawn from nature, it will be easyto decide whether the spots seen in any case a
. Hardwicke's science-gossip : an illustrated medium of interchange and gossip for students and lovers of nature . <:~ Fig. 148.—Leaf of Sycamore, with black ungus spots. FUNGUS SPOTS ON SYCAMORE LEAVES. IN answer to the inquiry that was made in one of thenumbers of Science-Gossip as to the cause ofthe spots on sycamore leaves, several have beenalready suggested. The most frequent cause of spotson the leaves of that tree is the fungus which Ipurpose to describe in this article. With the aid ofthe figures I have drawn from nature, it will be easyto decide whether the spots seen in any case are dueto this or any other source. The same fungus occurson maple leaves, and similar spots, due to an alliedfungus, are not uncommon on willow leaves. The fungus to which I refer is Rhytisma Fig. 149.—Melasmia acerina (section through a spermagone}.X 70. it advances. Ic is confined to the yellow spot; inthe still green parts of the leaf no mycelium can bedetected. So far the epidermis of the leaf has remained un-affected. But now certain parts of the interwovenmycelium or hyphasma begin to arrange themselves HARD WICKE S S CIE NCE-GO SSI P. 229 for the production of sporules. The first sign of thisis seen in the appearance on the upper surface of theleaf of small round black dots, which arise from abrownish discoloration of the cuticle. Beneath eachof these an hymenial layer is formed by the up-turning of the ends of the mycelial hyphas. Theseupturned ends assume the function of basidia, thatis, each produces a little bud from its extremity,which enlarges and takes the form of a slightlyflexuous cylindrical rod. When complete, this rod is yellow border. But though the surface of the spotmay appear to the eye uniformly black, yet on hold-ing the leaf up to the light, the
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectscience
