OBSERVATIONS.
Guignard and Strasburger found that in Idium and in Allium the pollen-grain after reduction, undergoes subsequent mitoses, in each of which the same reduced number of chromosomes is re tained. This led Overton to suggest that reduction in the higher cryptogams, where sexual and asexual generations alternate, might take place as far back as the formation of the spore. He also suggested that all of the cells of the sexual generation might have the reduced number of chromosomes, and in 1893 he strength ened his position by showing that the cells of the endosperm in the Gymnosperm Ceram:4mila, divide with the reduced number. But it was Strasburger (1894) who proved it, beyond doubt, by showing that in the fern 017111171da all the cells of the prothallus have the reduced number of chromosomes ; in other words that all cells derived from the spore have half as many chromosomes as the cells of the asexual generation. Reduction in ferns, there fore, takes place during the formation of the spore and here, if anywhere, we must look for the tetrads.
A. -Water/al and Kratzon.—Two fern species (Pteris trennela and Adianturn crineatitin) were selected, which were found in a fernery in October, to be in various stages of spore-formation. The pin nae were removed and cut into small pieces before fixation. The fixing agents used were 1, Herman's platino-aceto-osmic mixture ; 2, Von Rath's fluid ; 3, corrosive sublimate ; 4, sublimate-acetic; and 5, picro-acetic. The best results were obtained with I, 3 and 4. The pieces were imbedded in paraffine and cut horizontally in sections about 4 to 5 p thick. The stains used were Heidcnhain's haematoxylin, either alone or with orange G or Congo red as counter stains in the majority of preparations, although Flemming's triple stain gave good results.
B. Te•minology.—In animals three periods are recognized in the development of the reproductive cells (0. Hertwig). i. A " di vision period," during which the primordial germ cells (" and " spermatogonia ") increase by ordinary mitoses; 2, a " growth-period," during which the primordial germ cells enlarge and during which tetrads are formed. These cells are known as " primary oOcytes " and " primary spermatocytes," and 3, the " maturation-period," during which the nuclei with tetrads are divided by mitosis into nuclei with dyads (" secondary okytes " and " secondary spermatocytes"). These are again divided to
form eggs or spermatids.
As regards the periods of maturation it can now be shown that both male and female cells in many animals, and reproductive cells in some plants (Pteridophytes), conform to the same type. It is well known that in spore formation of Pteris, the single primor dial cell ultimately gives rise to sixty-four spores. It is also known that there are sixteen so-called " spore-mother-cells " in each spor angium, and that from these sixteen cells the final spores are formed. The stage between the first spore cell and the sixteen cells is directly comparable with the " division-period " in animal maturation. The sixteen-cell stage (see next page) is the stage of enlargement and of tetrad-formation and corresponds with the "growth-period." Finally the " maturation-period " is recognized by the two consecutive divisions of the sixteen cells to form the sixty-four spores.
As the maturation phenomena are so closely parallel in plants and animals, it would be of advantage to have the corresponding cells designated by analogous names. In some cases the present botanical names are unwieldy and inappropriate. The " spore mother-cell " as a designation for the cells of the sixteen-cell stage is incorrect as well as clumsy ; for, if we consider the nuclei alone, these cells do not give rise to the spores, but to the " mother-cells " of the spores, and are therefore the " grandmother-cells " of the spores. I propose, therefore, to use the term " primary sporocyte " for the cells of the sixteen-cell stage, and " secondary sporocyte " for cells of the thirty-two-cell stage. These terms are directly analogous to " primary" and " secondary" " oecyte," and " sperma tocyte" in animal cells. The term " sporogonium," which in this connection would be analogous to the term " agonium " or " sper matogonium " is, unfortunately, already used in a different sense in botanical nomenclature and I shall therefore designate ,the first eight cells in spore formation as " archesporial cells" in accordance with botanical usage.