Studies in Spirogyra

Part I. Variation in S.cataeniformis. S. cataeniformis has been investigated in order to find whether there is any relation between the range of variation it shows, and the season of the year. Cell length. The range in variation of cell length, and an expression for the mean cell length, has been determined statistically at fortnightly intervals during twenty months.The method adopted was as follows: a standard length of filament was chosen and the number of cells in this length was determined for 200 filaments; and the maximum, minimum, and average length of cell, present in four cells of these 200 filaments, was recorded. Chloroplast. Records have been made of the following: (1) the range in variation of the number of chloroplast turns per cell; (2) the maximum, minimum, and average number of chloroplast turns per cell; (3) the relation between the number of chloroplast turns per cell, the length of cell, and the number of pyrenoids per cell. Micro-chemical reactions. At various times of the year the starch and oil content of the cells and the nature and reaction of the cell wall have been recorded. It has been found that with regard to all these characters S.cataeniformis shows no seasonal variation. In spite of a well marked periodicity the range in form and structure of the cells is approximately the same at all times of the year. Part II: Conjugation in Spirogyra. An attempt has been made to discover the way in which the filaments of Spirogyra become laced together during conjugation. At the present time there exist two essentially different descriptions of the early stages of conjugation. In one, the two filaments are said to be parallel to each other, and the opposing cells to send out papillae which grow towards eachother till they meet and fuse. In the other, the two filaments are said to lie in contact, and are pushed apart by the growth of papillae from opposing cells.Three species of Spirogyra have been investigated: S.weberi S.varians, and S.cataeniformis. Special methods of culture were employed so that the conjugating filament pairs could be watched, under nearly natural conditions, from an early stage of conjugation to a later stage. Drawings of these stages have been made with camera lucida, and photographs have been taken. In all three species has been found that the filaments first lie in contact, and are later pushed apart by the growth of papillae from opposite cells; the first formed papilla may arise in either of the conjugating filaments and is independent of sex. The position of the nucleus in the cells, the relativesize of the conjugating cells, and the growth in length of the cells during conjugation have been described.