PROF. NORDENSKIOLD, EXPEDITION TO GREENLAND. 397 



taken as the standard for the number of cells in the separate 

 tlu'eads is accounted for by the regular continuous bisection of the 

 cells, whereby their propagation proceeds. The connexion between 

 the cells is the looser the older the partitions become, as the older 

 membranes assume a looser consistence. In a thread of 16 cells, 

 the connexion between the eighth and ninth cells is soon broken, 

 and in the two threads thus resulting the connexion between the 

 fourth and fifth cells is weaker than that between the second and 

 third or the sixth and seventh. The threads therefore often lie 

 bent at an angle. The diameter of the cells is O'OOS — 0*012 mm., 

 and their length 0-016 — 0*040 mm. Individual cells may some- 

 times attain a length 0*055 mm. and a breadth of 0'015 mm., 

 whereas a great number of other single cells are met with of very 

 small dimensions, from spherical forms of only 0*006 mm. diameter 

 to those of ordinary form and size. As the ends of the cells, where 

 they are joined together, are rounded, there is, of course, a con- 

 traction between them, which becomes more and more conspicuous 

 .is the connexion betAveen them is loosened by time. The mem- 

 brane is thin and hyaline, and its outermost layer (the remnants of 

 the membranes of the mother-cells altered after division) is of an 

 almost slimy consistence, whereby the cells are for some time kept 

 together. The contents of the cells are in part concealed by a dark 

 purple-brown colouring-matter^ which in dried cells is immediately 

 drawn out on wetting them. The centre of the cells is occupied 

 by an oblong or cylindrical mass of chlorophyll, of somewhat 

 irregular contour, in the extremity of which two nuclear rounded 

 bodies are imbedded, which in general cannot be perceived by the 

 eye till the colouring-matter has been removed by means of re- 

 agents. We sometimes meet with four such bodies in a cell, 

 sometimes only one : the former a result of accidentally checked 

 division of the cells ; the latter of such division having lately 

 taken place. In the liquid of the cells a number of small grains 

 are found, which are for the most part collected round the peri- 

 phery of the cell or at its ends. 



" Judging from the construction of the cells, and the manner 

 of their multiplication, the Alga before us appears to belong to 

 the ConjugatcB ; but as I have not succeeded in discovering fruc- 

 tification in it, it would be rash to decide to which genus it is to 

 be referred. The thread-like rows of connected cells agree with 

 the Zygnernacece ; whereas, on the other hand, an unmistakable 

 likeness to the DesmidiacecB, especially Cylijidrocystis, and the 

 nearly related genera, is indicated by the strongly marked divisions 

 into multiples of two, and by the tendency of the rows of cells to 

 fall asunder, as far as the destructibility of the uniting cell-mem- 

 branes permits, into parts consisting of cells united in pairs, which 

 however is seldom possible, in consequence of the greater energy 

 possessed by the power of multiplying the cells. As the above- 

 mentioned small single cells, which occur in great numbers, are 

 much less in diameter than those cells which arise from the bi-scc- 

 tion of the threads, they have perhaps a different origin from these 

 latter, although the researches which I have hitherto been enabled 

 to devote to this subject have not furnished any illustration of it. 



