PRINGSHElMj ON CHRONIZOOSPORES OF HYDRODICTYON. 105 



families formed by individuals reunited into one unicellular 

 plant ; and in this view I entirely coincide. 



On the other hand, by their processes or appendages, in 

 the form of horns, the polyhedrons of Hyclrodictyon denote 

 its aflfiuity with those small kinds of uly<2 whose cells, at all 

 events on their free side, are furnished with similar append- 

 ages. Of this number are Pediasirum (INIeyer), the Co'lestrum 

 (Noge), Sorastrum (Kiitz), and Scenedesmus (INIeyer), which 

 on account of their appendages have been wrongly classed by 

 some morphologists amongst the Desmidiacese. They form, 

 in common with Hydrodictyon and some other types, as yet 

 but little known, a special family, which may be called that 

 of the liydrodictyese. 



To the important characters drawn from the mode of mul- 

 tiplication and the association of individuals into families 

 similarly grouped, showing a strict analogy of Hydrodictyon 

 with the DesmidicEe, we have now to add this other mark of 

 external affinity, and which is only met with in individuals 

 destined to an isolated life ; for the appendages are more de- 

 veloped, except at those points of the cells v/hich are intended 

 to unite themselves to other cells, or to be prolonged into 

 processes, if this union does not take place. Frequently, 

 the first-born cells of the polyhedrons evince an unequivocal 

 tendency to produce appendages. When, indeed, the new 

 network, instead of forming a complete sac, only constitutes, 

 as I have before said, a single cellular layer, in the manner of 

 Pediasirum periusum, then the peripheral cells or those 

 which are associated in great irregular masses, and 

 above all, those which are joined to at least four of their 

 neighbours, produce usually two appendages, and in this 

 respect resemble exactly the peripheral cells of Pediastrum 

 bory anion. 



After all this, it can scarcely be doubted that the different' 

 genera cited above, as plainly analogous to Hydrodictyon, must 

 present similar developmental phenomena. 



Two sorts of zoospores have been recognised in Pediastrum, 

 the largest of which, according to Braun, re-attach themselves 

 after their birth to the new family, Avhilst the smaller ones, 

 observed for the first time by M. Bary, are dispersed and remain 

 isolated. The ultimate fate of the latter remains still un- 

 known; yet if the vegetation of Pediastrum be compared 

 with that of Hydrodictyon, it seems obvious that the micro- 

 spores of the former are in reality its chronizoospores 

 {Dauerschivaemner) . 



The same morphological value must be given to the micro- 

 spores that I have seen dispersed in Coelastrum, whilst its 



