316 RECOED OF CURRENT RESEARCHES RELATING TO 



division at right angles to the longer diameter of the cells (Coleo- 

 desmium, Tolypothriot, Hilsea, Scytonema), or by both longitudinal and 

 transverse division (Stigonema, Hapalosiphon, Capsosira). 



2. The increase of the colonies takes place by the formation of 

 " pseudoramuli " and true branching, or by fracture. 



3. The pseudoramuli are portions of filaments which deviate from 

 the ordinary direction in consequence of the interposition of heterocysts 

 (Tolypothrix), or without their intervention (Hilsea, Scytonema). 



4. The formation of pseudoramuli may be regarded as a process of 

 multiplication by means of immobile fragments, which are sometimes 

 capable of isolating themselves and developing independently into 

 new colonies (Hilsea, Scytonema sp., Tolypothrix sp.). 



5. In the genus Coleodesmium the increase of the colony is effected 

 by spontaneous fraction of the filaments ; the difterent portions 

 remain united in a bundle within a common gelatinous envelope, where 

 they increase independently. 



6. True ramifications originate from repeated division of any cell 

 in the series, in a direction at right angles to the last division 

 (Stigonema, Capsosira, HapalosipJion). 



7. All the Scytonemacese multiply by means of mobile fragments 

 or hormogonia, or by spores. 



8. The hormogonia are set at liberty by the dissolution of the 

 gelatinous envelope, when the filament breaks up into fragments, 

 each of which becomes a hormogonium ; or by the whole of the fila- 

 ments becoming transformed into hormogonia. 



9. The hormogonia move slowly in the water in a rectilinear 

 direction ; light exercises no influence on their movement. 



10. During germination the hormogonia are enclosed in a delicate, 

 transparent, mucilaginous envelope, while breaking up into portions 

 of various lengths [Tolypothrix, Coleodesmiihm, Scytonema sp., Sti- 

 gonema sp., Capsosira), or each is completely transformed into a new 

 colony without breaking up (Scytonema sp., Stigonema sp.). 



11. During the transformation of an entire hormogonium, or of 

 each fragment of one, into a colony, one of the two apical cells of 

 the filament becomes a heterocyst, except in Coleodesmium. 



12. The spores are isolated cells capable of resisting cold and 

 excessive drought ; they germinate after a certain period of rest. 



13. During germination the exospore bursts transversely to give 

 exit to the internal germ. 



The Scytonemaceas may be classified as follows : — 



A. The cells divide transversely only. Tribe I. Scytonemeoe. 



a. No pseudoramuli ; filaments united in a bundle within 

 a common envelope. Subtribe 1. Coleodesmiece. Genus 

 1. Coleodesmium Bzi. 

 h. Pseudoramuli ; filaments free, or rarely in proximity 

 laterally, but not united in a bundle within a common 

 envelope. Subtribe 2. Euscytonemece. 

 a. Colonies c^spitose, and with definite growth ; pseudo- 

 ramuli with 1-3 heterocysts at the base. Genus 2. 

 Tolypothrix Ktz. 



