SPIROGYRA. 



[ 597 ] 



SPIROGYRA. 



Spirogyra communis. 



Fragments of two 



filaments conjugating. 



Magnified 200 diameters. 



The laminated struc- 



stages throughout the green band. A remark- 

 able lenticular nucleus 

 is also present sus- Fig. 673. 



pended in the centre of 

 the cell by threads of 

 protoplasm running 

 out to the primordial 

 utricle lying against 

 the cell- wall. Some- 

 times this nucleus is 

 placed with its faces 

 towards the side wall 

 (S. nitida, PL 5. fig. 

 26), sometimes it ap- 

 pears to be placed with 

 its faces looking up 

 and down, as it pre- 

 sents the appearance of 

 a narrow ellipse when 

 seen sideways (S. pel- 

 lucida, PL 5. tig. 27). 

 ture of the cell-walls is also curious, but 

 will be better understood after a sketch of 

 the mode of development. 



The attractive appearance of the Spiro- 

 gyrcB and the easily observed phenomenon of 

 conjugation have caused much attention to 

 be paid to this genus, and many points of 

 their history have been determined. The 

 cells composing the filaments all multiply 

 simultaneously when the plant is growing, 

 each becoming twice its length and dividing 

 into two. It has been certainly observed by 

 A. Braun and Pringsheim that the division 

 is preceded by a division of the nucleus. 

 From this interstitial mode of growth it is 

 evident that the walls of the cells of plants 

 actively vegetating must soon become com- 

 posed of a number of layers belonging to 

 distinct generations of cells. Thus, supposing 

 we have an original cell a, this encloses its 

 progeny, two cells a 2 & b, and when these 

 divide again and come to enclose respectively 

 a 3 & c and V* & d, the parent-cell a, 

 stretched to four times its original length, 

 still encloses the whole. The laminae belong- 

 ing to the respective generations do not 

 become very intimately blended, for by ma- 

 ceration we may cause the outer membranes 

 to soften and dissolve, and set free the 

 younger cells intact. The older membranes 

 seem to have become thinner by stretching, 

 or by solution, midway between their septa, 

 since on maceration we may often see them 

 give way in the middle, and the young cells 

 slip out from them, leaving them as short, 

 hyaline tubes with a diaphragm in the middle. 

 The ends of the cells of some species gene- 



rally present a curious appearance, which 

 might be compared with the " punt " of a 

 bottle, only it is a circular fold thrown in 

 from the cross septum. It is attributed to 

 the excessive growth of the membrane of the 

 young cells, confined in space by the outer 

 parent-membrane. The filaments of Spiro- 

 gyra are consequently very instructive in 

 reference to vegetative cell-formation. In 

 some cases the half-dissolved parent cell- 

 membranes form a delicate, but well-defined 

 gelatinous coat on the tube (PI. 5. fig. 27 s). 

 The reproduction of this genus exhibits, 

 besides the proper conjugation, other phaeno- 

 mena, the import of which is not yet fully 

 determined. The conjugation itself has been 

 observed by almost every microscopist. It 

 consists essentially here in the production of 

 papillary elevations on the contiguous walls 

 of the cells of two filaments lying side by side ; 

 the growth of these papillae until they come in 

 contact ; and their coalescence so as to form 

 a canal of communication between the two 

 cells (fig. 6/3. PL 5. fig. 18). When this is 

 accomplished, the contents of one of the 

 cells (the contents of both having meanwhile 

 lost their characteristic arrangement on the 

 cell -walls) pass over through the cross tube 

 into the other cell, when the contents of 

 both become blended and form an elliptical 

 free body (PL 5. fig. 18), which acquires 

 cellulose integuments and becomes a spore, 

 lying free in the parent-cell. This process 

 is accompanied by the death of the parent- 

 filaments, conjugation often taking place in 

 the majority of the cells; the spores are 

 sometimes set free by decay of the parent 

 cell-wall, but very often the latter remain 

 undissolved until the germination of the 

 spore (PL 5. fig. 19). A modification of this 

 mode of conjugation takes place in some 

 cases, apparently as an abnormal process, for 

 it has been observed (Braun) taking place in 

 those species which conjugate as above. It 

 occurs in solitary filaments, in which two 

 contiguous cells produce papillae at the ad- 

 joining ends, growing towards each other 

 and coalescing, the contents of one of the 

 cells thus passing into the next cell of the 

 same filament. A. Braun calls this " chain- 

 like" conjugation, in contradistinction to 

 the "ladder-like" conjugation above de- 

 scribed. As it occurs associated with this, 

 Kiitzing's genus Rhynchonema, founded upon 

 it, cannot stand. 



The ripe spore presents the appearance of 

 j an elliptical body enclosed in three membra- 

 j nous coats, the outer of which is of delicate 



