416 Annals New York Academy of Sciences 



of elongate, epiphytic unicells contained in thin gelatinous sheaths and at- 

 tached to the substratum by basal developments of the sheath. The entire 

 protoplast is found to divide into a uniseriate chain of rounded or compressed 

 spherical cells which usually remain united by their membranes. As the cells 

 enlarge, the trichome then bursts through the sheath of the mother cell, and 

 the cells upon dissociation from each other then elongate into a new unicell 

 and secrete new sheaths. The family is represented by two small genera, 

 Clastidium and Stichosiphon, each containing one species. 5. sansibarkus 

 (figure 3), has a smooth apex, whereas plants of C. setigerum terminate in a 

 spinelike projection of the sheath at the apex. 



Plants of the Stigonemataceae are floccose, feltlike, cushion-shaped, or 

 spherical. The filaments are free or imbedded in a gelatinous matrix, the 

 trichomes are branched, and the cells are uni- or multiseriate with division 

 occurring in planes perpendicular to or parallel with the axis of the filament. 

 Heterocyst formation is random, intercalary or terminal on short branches. 

 Cell division in planes perpendicular to the axis of the trichome is followed by 

 a growth in length of cells at filament apices which forms the resulting elongate 

 and branched filaments. Cell division also occurs in planes parallel to the 

 axis of older filaments with consequent increase in diameter and in the forma- 

 tion of subsequent branches. Reproduction is by fragmentation. The family 

 is represented here by Stigonema panniforme (figure 4). Members of this 

 genus have filaments which soon develop multiseriate cells connected by proto- 

 plasmic strands. Other prominent genera include Capsosira which has up- 

 right and parallel filaments that form compact cushion-shaped plants, Nosto- 

 chopsis which has radial filaments within a gelatinous matrix of coalesced 

 sheaths and develops intercalary, pedicellate, or sessile heterocysts, and Hapa- 

 losiphon and Fischerella which contain trichomes of uniseriate cells except in 

 the older basal portions of the plant. The latter two genera also exhibit 

 scytonematoid branching. 



The Nostocaceae contain aquatic or terrestrial plants which are free or at- 

 tached to a substratum. The sheaths are mucous, gelatinous, membranaceous, 

 or well hydrolyzed and absent. Trichomes are unbranched, frequently twisted 

 and entangled; all of the cells divide at relatively the same time, and inter- 

 calary or terminal heterocysts are present. Reproduction is by fragmentation 

 or by spores that are formed in most species. The trichomes of Anabaena are 

 free or form a fragile layer; the matrix is composed of hyaline, hydrolyzed 

 sheaths. Spores are variously situated in relation to the heterocysts. Tri- 

 chomes of planktonic Raphidiopsis and Aphanizomenon resemble those of 

 Anabaena except that the end cells are pointed in Raphidiopsis and colorless in 

 Aphanizomenon. Trichomes of Nostoc, and Wollea develop within a gelatinous 

 matrix of definite shape; all cells may apparently become spores or hetero- 

 cysts. In species of Nostoc, e.g., N. muscorum (figure 5), the trichomes 

 become much contorted, whereas i^ Wollea they are relatively straight. Cylin- 

 drospermum has comparatively short trichomes with terminal, solitary hetero- 

 cysts and adjacent spores. Cells and spores of Nodularia are compressed or 

 disciform in rather straight trichomes. Hydrocoryne, a rarely collected species, 

 apparently forms no spores and has discrete although readily hydrolyzed cylin- 

 drical sheaths. 



