Page:Bulletin of the Torrey Botanical Club 30 214-224.djvu/12

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Howe and Underwood: The Genus Riella

spores. The involucres are less globose and more pointed at the apex than those of R. Cossoniana. Judging from two specimens of R. Cossoniana collected by Professor Trabut, R. affinis has the appearance of being a larger species with broader lamina, though this might not appear from a comparison of the measurements given above with those given by authors for R. Cossoniana. Our specimens of R. affinis are prostrate and more or less entangled with mud and are so delicate and fragile that it is quite possible that the measurements in the above description may fail to do full justice to the height of the plant. It may be remarked that in occasional capsules the spores though showing a well-developed brown coloration have short spines or papillae much like those of R. Cossoniana; such spores are always smaller than is normal for the species and are probably immature or else have ripened under abnormal conditions.

Our experiments in germinating the spores of Riella affinis have been more successful than those with the spores of Riella Americana, though they were not begun until December, 1902, five and a half years from the date of collection of the specimens. More than half of the spores experimented with germinated in a few days by being placed on a piece of wet filter-paper in a glass dish kept in a moist chamber at ordinary living-room temperatures. The germ-tube in practically all cases emerges, as in R. Americana, from the outer or more spiny face of the spore, usually near its middle. The root-hair follows a little later, its lumen remaining continuous with that of the germ-tube. The length of the germ-tube varies exceedingly. Finally, there appears in it a somewhat curved transverse wall with its convexity turned toward the spore. The part above contains most of the starch grains and in the course of time begins to show chlorophyll, cell-divisions meanwhile taking place as described above for R. Americana. The length of the germ-tube from the spore-wall to the curved septum has been observed to vary in different cases from 0.02–0.7 mm. One or two root-hairs, in addition to the one which comes from the base of the germ-tube, may spring out later from some part of the filamentous stalk of the young gametophyte. The forms assumed by the young gametophytes are extremely varied and are doubtless determined to a considerable extent by the conditions of