INVERTEBEATA, CRYPTOGAMIA, MICROSCOPY, ETC, 317 



/?. Colonics witli indefinite growth ; pseudoramuli not 

 connected by heterocysts. 

 * Pseudoramuli very soft and delicate, produced 

 irregularly, sometimes joined laterally, or 

 united in a bundle. Genus 3. Hilsea Kirchn. 

 ** Pseudoramuli in parallel pairs. Genus 4. 

 Scytonema Ktz. 

 Sect. 1. Petalonema. Envelope exceeding the 



internal filament, several lines in size. 

 Sect. 2. Euscytonema. Envelope smaller ; 



pseudoramuli free. 

 Sec. 3. Symj^hyosiphon. Envelope small ; 

 pseudoramuli more or less united laterally. 

 B. Cells dividing also longitudinally. Tribe II. Stigonemece. 



a. Filaments composed of a double or multijjle series of cells. 



Genus 5. Stigonema Ag. 



b. Filaments composed of a simple series of cells. 



a. Filaments erect or united into a pulvinate cushion of 

 definite size. Genus 6. Capsosira Ktz. 



fi. Filaments not united ; heterocysts solitary and 

 produced by direct transformation of any cell of a 

 series. Genus 7. Hapalosijjlion Nag. 



Development of the Conceptacle of Fiicaceae.* — T. 0. Bower 

 has been carrying on a series of researches on this subject, relating 

 to the genera Fucus, Himant Italia, Halidrys, and others, conducted in 

 Professor De Bary's laboratory at Strassburg. The materials were 

 treated, while fresh, with a dilute solution of chromic acid in water, 

 and afterwards preserved in alcohol ; others were preserved in a 

 saturated solution of common salt, and then hardened in alcohol. 

 The sections were in all cases mounted in glycerine and acetic acid. 



The formation of the conceptacle is preceded by the decay of one 

 or more cells which occupy a central position with regard to the 

 changes which follow. The number of cells thus removed is various, 

 and the manner of tlieir destruction is not constant, but the fact 

 remains in all cases. The cell or cells which decay arc all members 

 of a linear series. 



The diflerences in the mode of development, at least in the early 

 stages, depend on the diflerences in activity of tangential division of 

 the cells of the central series. In Fucus the terminal or initial cell 

 of tlie central series ceases to divide tangentially, and is left behind 

 by the surrounding tissue, and wlieu it decays, leaves a cavity which 

 extends further into tlie tissue than the base of the cells of the surround- 

 ing limiting tissue. 'J'hc tissue lining the cavity is therefore in this 

 case derived in its basal part from the cortical, in its upper part from 

 the limiting tissue. In Himanlhalia, on the other hand, the cavity 

 thus formed extends only at most to the base of the cells of the 

 limiting tissue ; the lower lining of the cavity is thus derived only 

 from the limiting tissue. 



* 'Qimrt. .Tniirii. Miry. Sci.,' xx. (1880) p. 30. 



