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A Study of Preissia quadrata
Mary Ellen O'Hanlon
Vol. 84, No. 2 (Oct., 1927), pp. 208-218
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/2470701
Page Count: 11
You can always find the topics here!Topics: Spores, Thallus, Sporophytes, Spore germination, Plants, Plant cells, Gametophytes, Mother cells, Tracheids, Quadrants
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1. Twelve to sixteen archegonia are borne in each female receptacle, usually three to four in each quadrant, although as many as six were counted in a single quadrant of a receptacle. 2. Although fertilization is probably 100 per cent, the number of mature sporophytes in a single receptacle varies from one to six, the average number for over 100 heads was 2.98, the dominant number being four sporophytes to each head. 3. The sporogenous cells which metamorphose into elaters seem to be sister cells to the spore mother cells; therefore the number of spores is four times the number of elaters. 4. The number of spores to each capsule was estimated at about 3000; the average number for each head, therefore, would be nearly 9000. 5. The spores, although much less numerous than in Marchantia, are decidedly larger. Their diameter is about 75 μ, while the diameter of the spore of Marchantia polymorpha is not over 18 μ. The elaters of Preissia are smaller than those of Marchantia, although their number is greater in proportion to the number of spores. 6. The spores of Preissia germinate readily on a solid substrate, and they are viable for a shorter time than the spores of Marchantia, as only about 10 per cent of them germinated four or five months after their maturity. 7. The method of spore germination is similar to that in Marchantia, in that there is a variety of initial steps, with even greater scope for variation and individuality in Preissia than in Marchantia. 8. Branching is very common, and in some cases two thalli are initiated from a single spore cell. Early branching is frequent. 9. Unlike Marchantia, there are no cells for the storage of essential oils in the young thallus of Preissia. 10. The rhizoids of the young thallus, relatively few in number, are of the plain walled type as in Marchantia. 11. As there is no definite midrib in the adult thallus of Preissia, the thickening in the middle of the young plant is more extensive than is the case in Marchantia. 12. The general contour of the advancing young gametophyte of Preissia is often quite irregular, since there are so many actively growing points. 13. As in Marchantia, a distinct apex with its marginal row of meristematic cells is conspicuous in at least one region of the young thallus. 14. Finally, as in Marchantia, there is no single cell functional in the development of the young gametophyte of Preissia that may be designated as the apical cell.
Botanical Gazette © 1927 The University of Chicago Press