PROCEEDINGS OF SOCIETIES. 



Dublin Microscopical Club. 



Vlth January, 1878. 



On the Development of the Siphons in Polysiphonia. — Dr. E. 

 Perceval AV^right exhibited some mounted specimens presenting 

 the form of apical growth so characteristically described by 

 Nageli in the ' Zeitschrift fiir wiss. Botanik,' 1836, and showing 

 in addition some new facts (as he believed) in the development 

 and growth of the so-called siphons in Polysiphonia. The 

 species selected was one with four siphons, representing the 

 subgenus Oligosiphonia. Such a species would be described as 

 having a " frond consisting of four tubes radiating round a central 

 cell, and generally containing endochrome " (Harvey), or, as by 

 Agardh, in some detail, as " Cellulao istse periceutrales, quas 

 siphones vocant, sunt endochroraate colorate repletse, parietibus 

 hyalinis crat^sis, polystromaticis invicem et a cellulis articulorum 

 proximorum separatee." But all such-like descriptions appeared 

 to Dr. Wright to be based on a misconception of the structure to 

 be seen when the living plant is carefully studied, and when 

 quite fresh specimens are submitted to the action of re-agents. 

 It then become s pretty evident that the growing filament in 

 Polysiphonia is in reality one continuous cell bounded on all 

 sides by its own well-marked cell- wall, that below its growing 

 point, below the layer of homogeneous protoplasm, and below 

 even that so-called granular protoplasm of Nageli, there exists a 

 protoplasm, which has, as it were, taken up its maximum quan- 

 tity of water of organisation, has become a viscid, almost sensi- 

 tive substance, capable of forming out of itself chlorophyll and 

 starch-granules, and, on occasions, exhibiting, in some allied forms, 

 all the characteristic movements of animal pseudopodia. In this 

 layer the siphons originate. In the species exhibited the process 

 was — (1) a thin lozenge-shaped plate of the protoplasm became 

 detached all but in five parts, where the thread-like continua- 

 tions kept the little lozenge of protoplasm from felling away 

 from the upper portion ; (2) this lozenge increased greatly in 

 thickness,and after a certain thickness had been attained, it divided 

 asunder into a central portion and four equi-dimensioned peri- 

 pheral portions ; each of these latter still attached to the central 

 portion by prolongations from the centre of their long diameter 



