114i ANATOMY AND PHYSIOLOGY OF 



of the two cells are exactly similar ; sometimes all the cells of 

 one filament take away the contents of the cells of the other ; 

 sometimes this happens only to a part of the cells, while the rest 

 empty themselves into the cells of the second filament ; and some- 

 times spores are formed in cells which have not copulated, all 

 this taking place v^ithont any definite rule. 



Copulation has recently been discovered in many uni-cellular 

 Algge, in particular by Morren in ClosteTium {^^Ann. d,Sc. nat. sec. 

 ser," V. 2 57), by Ealfs, in the Desmidiacese, and by Thwaites (^'Ann. 

 of N'at Hist" XX. 9, S48) in the Diatomacese. Eemarkable as the 

 whole process of copulation is, its product is, in many respects, 

 enigmatical in no less degree. In the copulation of uni-cellular 

 Algse, two new individuals are generally formed; thus there is no 

 increase connected with this Biode of piopagation, but frequently 

 only one new individual is formed, and thus is presented the 

 strange phenomenon of a propagation resulting in a diminution 

 of the number of individuals, since the copulating individuals die. 

 In the Diatomaceae, moreover, ,the individuals produced by copu- 

 lation are much larger than their parents. In the majority of 

 copulating Algse, particularly in the Desmidiacese and Zygnemece,^ 

 the spore produced fi:om the union of the contents of the two cells 

 has not yet been seen to germinate, and it is not impx^obable that 

 it ought to be regarded, not as a spore, but as a sporangium, that 

 is to say, as a cell, the contents of which become developed into 

 numbers of germs (See AgSuxdh, ^^ Ann., d. Sc.nat sec. Ser" m, 197; 

 Hassall, '^Brit Fresh-water Algm,'' 24; Ralfs, ^'Desmidiece/' 10). 



In by far the greater number of the Algse, the spores are not 

 formed by copulation, but in single cells, either, as in the lower 

 forms, in the vegetative cells towards the close of their existence, 

 or in special fructification cells. 



The spores of a very large number of Algse, either before their 

 exit from the parent-cell, but principally in the period just succeed- 

 ing the emission, exhibit a movement, which is often very rapid. 

 These movements have not unfrequently been taken for animal, 

 voluntaiy motions, and have given origin to the most fabulous 

 conceptions concerning the transformation of animals into plants. 

 We owe the first extensive and aecm-ate observations on these 

 moving spores to the younger Agardh ("Ann. d. Sc. nat sec. Ser!' 

 vi. 193), who called them Zoospores. According to his researches, 

 they occur in the N'ostocJdncce,OscillatoricB, OonJ-crvece, Conjugatce^ 

 EctocaTpcm, Ulvacece^ and SiphonccB. The following is his account 

 of their development. During the later periods of the growth of 

 the cells, the chlorophyll, which in the young cells of these plants 

 forms a homogeneous mass, becomes transformed into globules, 

 which towards the close of the cell's life assume a spherical shape, 

 become detached from the wall of the cells and balled together in 



* Erroneous in regard to Zyncmese, see Yaucher, Meyer, and, more 

 recently, Fringsheim. Flo'ia, Aug. 1852 — A, H. 



