CHROMOSOME NUMBERS IN CHEILANTHES, NOTHOLAENA, LLAVEA AND POLYPODIUM

The chromosome numbers of 10 previously uncounted species in Cheilanthes and 1 species of Notholaena are reported. Several confirmatory counts are also listed. One of the plants, Cheilanthes parryi, should probably be retained in the genus Notholaena. Four plants are sexual diploids, three are diploid apomicts, four are triploid apomicts, and three are tetraploids. THE CHROMOSOME number not only informs us of the level of ploidy in a particular taxon, but it may lead us to infer the absence or presence of hybridity and/or apogamy. Triploids in ferns are notoriously correlated with both of these phenomena. In the absence of triploidy but in the presence of univalents in meiotic figures, we are sometimes able to infer the correct parentage of the cross. Ferns lend themselves very well to various types of analyses and the determination of the chromosome number is, therefore, one of the first steps in determining the evolution of certain taxa. MATERIALS AND METHODS-The taxa employed in this study are listed in Table 1. Voucher specimens of these plants have been deposited in the herbarium of Michigan State University. Meiotic material (young sporangia) was fixed in Carnoy's solution and squashed in Belling's aceto-carmin stain. For mitotic material (root tips) pot-bound plants were placed in a larger pot (two sizes larger) filled with wet peat moss to stimulate new root growth and, consequently, mitotic activity. New, white root tips were treated in a saturated solution of paradieblorobenzene in a refrigerator (5 C) for from 3 hr to overnight. They were then fixed in Carnoy's solution, hydrolyzed 22 min in 1 N HCI and stained in Feulgen's reagent. The tips were left in the latter fluid until they had stained sufciently, sometimes overnight. Squashing the Feulgen-stained tips in a drop of Belling's acetocarmine gave a better picture of the chromosomes. A slight boiling of the corner of the slide after the cover slip was in place also intensified the stain. Slides which showed promise were placed upside down on two glass rods in a petri dish and flooded with a mixture of one glacial acetic acid and four parts of absolute 'Received for publication May 19, 1966. The aid of the National Science Foundation (GB4630), the advice of Dr. Deran Markarian, and the technical assistance of Thamby Ninan, Joyce Nakamura, Claire Kelsch, and Julie Hitt are gratefully acknowledged. ethyl alcohol. Cover slip and slide were recombined in diaphane, set aside 4-8 hr, and then weighted with a lead weight. RESULTS AND DISCUSsION-According to Copeland (1947), there are 180 species in the genus Cheilainthes. Some of these should properly be returned to other well-known genera. Up to the present time 23 of these species have been examined cytologically. The results presented in this paper add 10 taxa which were previously uncounted. Notholaena, included by Copeland in Cheilanthes, has had only five members counted cytologically. Llavea is a monotypic genus and only additional cytotypes are possible. Polypodium with its 75 species has had over half of its species counted. The chromosome numbers listed in Table 1 and discussed below should not be regarded as final for the individual species because many fern species have cytotypes and these may be discovered by further investigatioln. Leptosporangiate ferns generally have 16 spore mother cells per sporangium and therefore produce 64 spores per sporangium after the two divisions of a normal meiosis. The spores are typical in appearance and viable. A taxon exhibiting this series of events is known as a sexual species. It has been found, however, that in many ferns the last of the synchronized premeiotic mitoses in the sporangium is abnormal. The chromosomes are duplicated but fail to separate into daughter cells with the result that only eight mother cells are formed, each with the 4n number (usually) of chromosomes. Normal meiosis then takes place in two stages and 32 normal spores are formed in each sporangium, each spore havingthe 2n number (usually) in its nucleus. The spores germinate to produce gametophytes each cell of which has the same number of chromosomes as the sporophyte. Gametophytes arising from a type of spore described above are usually deficient in archegonia so that there can be no true sexual reproduction. The