146 



FAMILY IV. PITHOPHORA.CEJ3. 



Chlorophylliferous Cladopliora-like Fresh-water Algfe, con- 

 sisting of celly formed by bipartition of the terminal cell, the 

 thallus having two distinct parts (1) the cauloid part, 

 developed from the germinated spore upwards, propagative, and 

 almost always branched, the branches placed a little space 

 below the top of their supporting cells ; (2) the rhizoid part 

 developed from the germinated spore downwards, almost always 

 sterile and branchless, commonly unicellular. Spores neutral, 

 quiescent (agamo-hypnospores), generally cask-shaped, single, 

 formed bv division into two of the cauloid cells, of the chloro- 



v 



phyll filled, and commonly widened upper parts of these cells ; 

 in germinating, as a rule, dividing into two cells, the one 

 giving rise to the cauloid and the other to the rhizoid part 

 of the thallus. Wittrock, Monograph of the Pitliophoracece, 

 p. 46. 



For full details of this Family, consult Prof. V. B. Wittrock " On the 

 Development and Systematic Arrangement of the Pithophoracea3 " (pub- 

 lished in English). Upsal, 1877. 



GENUS 63. PITHOPHORA. Wittr. (1877.) 



Character the same as that of the family given above. 



The formation of spores is effected in the following manner: The 

 tipper part, ^-^ of the mother cell of the spore, is somewhat widened. 

 The chlorophyll-coloured protoplasm in the low r er, not widened, part of 

 the cell then passes little by little into the upper and widened part, till it 

 is quite filled with chlorophyll-coloured protoplasm. A transversal cell 

 wall is then little by little formed just below the point where the 

 widened part of the cell commences. In this manner are formed one 

 lower cell containing but little protoplasm, almost devoid of chlorophyll, 

 the so-called subsporal cell, and one upper cell, rich in chlorophyll and 

 reproductive, the spore. Its shape is, as a rule, cask-like or cylindri- 

 cally cask-like. When the membrane of the spore has attained a not 

 inconsiderable increase in thickness the spore reposes some time befo-re 

 germinating, and consequently belongs to the class of spores which is 

 called hypnospores. With regard to its origin, it may be called an 

 agamo-spore, as being formed neutrally without any fecundation. 

 Formation of spores may take place in all the cells of the cauloid, in the 

 terminal as well as in the inclosed. As a rule it begins in the youngest, 

 i.e., the terminal cells ; afterwards proceeding downwards, or, in other 

 words, basipetally, in the principal filament as well as in the branches. 

 It is these spores which give origin by their germination to the course of 

 development already described. In this manner you will see one neutral 

 generation, forming hypnospores, follow upon another, in an uninter* 

 rupted series, without any metagenesis. 



