similar material occurs along branching and anastomosing tracts
through the protoplasm of the sporangium, giving rise to the
capillitium. The greater part of the lime granules pass out of the
protoplasm and are deposited in the capillitium, which in the ripe
sporangia of Badhamia is white and brittle with the contained lime
(cf. fig. 8). In this genus some granules are found also in the
sporangium-wall. Strasburger concludes that the sporangium-wall
of Trichia is a modification of cellulose (29).
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Fig. 8.—Sporangia of Badhamia panicea, some intact, others (to left) ruptured, exposing the black masses of spores and the capillitium. The latter is white with deposited lime granules. An empty sporangium is seen above. |
It has been stated (16), but the observation requires confirmation, that a fusion of the nuclei in pairs occurs early in the development of the sporangium.
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Fig. 9.—Part of a section through a young Sporangium of Trichia varia, showing the mitotic division of the nuclei (n) prior to spore formation. 𝑐, Capillitium thread. |
Fig. 10.—Part of a section through a Sporangium of Trichia varia after the spores are formed. | |
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Fig. 11.—Badhamia utricularis. 𝑎, Sporangia. 𝑏, Capillitium and cluster of spores. |
Fig. 12.—Physarum nutans. 𝑎, Sporangia. 𝑏, Capillitium threads, with fragment of the sporangium-wall attached, lime knots at the junctions and spores. |
At a later stage, after the capillitium is formed, the nuclei undergo a mitotic division which affects all the nuclei of a sporangium simultaneously. This was first described by Strasburger (29). While it is in progress the protoplasm of the sporangium divides, into successively smaller masses, until each daughter nucleus is the centre of a single mass of protoplasm.[1] These nucleated masses are the young spores. A spore-wall is soon secreted and the sporangium has now resolved itself into a mass of spores, traversed by the strands of the capillitium and enclosed in a sporangium-wall, connected with the substratum by a stalk. As ripening proceeds, the wall becomes membranous and readily ruptures, and the dry spores may be carried abroad on the currents of air or washed out by rain.
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Fig. 13.—Chondrioderma testaceum. 𝑎, Group of three Sporangia. 𝑏, Capillitium, fragment of sporangium-wall and spores. |
Fig. 14.—Craterium pedunculatum. 𝑎, Two Sporangia, in one the lid has fallen away. 𝑏, Capillitium with lime knots and spores. | |
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Fig. 15.—Didymium effusum. 𝑎, Two Sporangia, one showing the columella and capillitium. 𝑏, Capillitium, fragment of sporangium-wall with carbonate of lime in crystals, and spores. |
Fig. 16.—Lepidoderma tigrinum. 𝑎, Sporangium; the crystal-line disks of lime are seen attached to the sporangium-wall. 𝑏, Capillitium and spores. |
We may now review some of the main differences in structure presented by the sporangia. They may be stalked or sessile (fig. 13). If the former, the stalk is usually, as in Badhamia utricularis, the continuation of the sporangium-walls (figs. 11 and 12), but in Stemonitis and its allies (figs. 17 and 18) it is an axial structure. A central columella may project into the interior of the sporangium, either in stalked (fig. 15) or sessile (fig. 13) forms.
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Fig. 17.—Lamproderma irlaeum. 𝑎, Sporangia. 𝑏, A Sporangium deprived of spores, showing the capillitium and remains of the sporangium-wall. |
Fig. 18.—Stemonitis splendens. 𝑎, Group of Sporangia (nat. size). 𝑏, Portion of columella and capillitium, the latter branching to form a superficial network. | |
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Fig. 19.—Dictydium umblicatum. 𝑎, Group of Sporangia, nat. size. 𝑏, A Sporangium after dispersion of the spores. |
Fig. 20.—Arcyria punicea. 𝑎, Group of Sporangia. 𝑏, Capillitium. 𝑐, Spore. |
The sporangium-wall may be most delicate and evanescent (fig. 17), or consist of a superficial network of threads (fig. 18), which in Dictydium (fig. 19) present a beautifully regular arrangement.
In Chondrioderma (fig. 13) the wall is double, the inner layer being membranous, the outer thickly encrusted with lime granules. In Craterium the upper part of the sporangium-wall is lid-like and falls away, leaving the spores in an open cup (fig. 14).
- ↑ In some genera such as Arcyria and Trichia (illustrated in figs. 9 and 10) the division of the protoplasm does not occur until the nuclei have undergone this division. The protoplasm then divides up about the daughter nuclei to form the spores.
