SPIROGYRA. 



[ 716 ] 



SPIROGYRA, 



be compared to the "punt" of a bottle, 

 produced by 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. 9. 

 fig. 27s). 



The reproduction of this genus exhibits, 

 besides the proper conjugation, other phe- 

 nomena, the import of which is not yet fully 

 determined. The conjugation itself has been 

 observed by almost every microscopist. It 

 consists essentially 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 into contact, and their coalescence 

 so as to form a canal of communication be- 

 tween the two cells (fig. 668 ; PI. 9. fig. 18). 

 When this is accomplished, the contents of 

 one of the cells (the contents of both having 

 meanwhile lost their characteristic arrange- 

 ment on the cell-walls) pass through the 

 cross tube into the other cell, when the 

 contents of both become blended and form 

 an ellipitical free body (PL 9. fig. 18), which 

 acquires cellulose integuments and becomes 

 a spore or zygospore, 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 remains undissolved until the 

 germination of the spore (PI. 9. fig. 19). 

 A modification of this mode of conjugation 

 (PI. 3. fig. 24), occurs in some cases appa- 

 rently as an abnormal process; for it has 

 been observed (Braun) taking place in species 

 which conjugate as above. It occurs in single 

 filaments 'in which two contiguous cells 

 produce papillae at the adjoining ends, 

 growing towards each other and coalescing, 

 the contents of one of the cells thus passing 

 into the next cell of the same filament. 

 Braun calls this "chain-like" conjugation, 

 in contradistinction to the " ladder-like " 

 conjugation above described. As the two 

 forms occur associated, Kiitzing's genus 

 Ehynchonema and others founded upon this 

 are of doubtful value. 



The ripe spore or zygospore forms an 

 elliptical body enclosed in three membra- 



nous coats, the outer of which is of deli- 

 cate texture and separated by an interval 

 from the next, which is brownish and of 

 firm texture. The inmost coat or true 

 spore-membrane, is again delicate. The 

 spores appear to rest through the winter 

 | after they are formed, and to germinate in 

 | spring, in which process the middle coat 

 j of the spore splits at one end, longitu- 

 dinally, opening by two valves to allow the 

 inner to grow forth, which bursts through 

 the outermost sac, in the form of a tube 

 (PI. 9. fig. 19) which soon acquires the 

 characteristic appearance of the parent 

 plants. The contents of the spore are brown 

 and homogeneous during the stage of rest 

 (fig. 21) ; in germination they become green 

 again, and arrange themselves in the spiral 

 bands (fig. 22), which become more distinct 

 as the cell elongates. 



Certain other occurrences take place in 

 the cell-contents of the Spirogyrce, the rela- 

 tion of which to the reproduction is not so 

 clear as the above. In filaments in an un- 

 healthy condition, about to decay, such as 

 are often seen when a collection of them is 

 placed in a jar of water to keep for exami- 

 nation, it is not uncommon to see the green 

 contents gradually lose their spiral arrange- 

 ment and break up into a number of globular 

 portions (PI. 9. fig. 28) j we have sometimes 

 observed these rolling over slowly in the 

 cell. In one case we have observed the 

 contents converted into sixteen distinctly 

 organized biciliated zoospores (PI. 9. fig. 20), 

 differing only from the ordinary zoospores 

 of the Confervoids in the almost total 

 absence of colour. They were somewhat 

 crowded in the cell, and moved lazily about 

 in it, the cilia vibrating. It is still more 

 common to observe the contents of decayed 

 filaments converted into encysted globules 

 (PI. 9. figs. 24, 25), which appear to be 

 a kind of resting-form of the zoospores. 

 These globules, which have a tough spinulose 

 coat, have been observed by Pringsheim 

 as produced from the contents both of 

 ordinary cells, and abnormally ? from the 

 contents of a large spore (PI. 9. fig. 23) : the 

 latter case might give colour to the idea that 

 this was a sporange, had not its germination 

 been observed. Pringsheim has further 

 noticed that actively moving zoospores are 

 produced from the small encysted bodies ; 

 perhaps these may fulfil an antheridial 

 function. Carter has observed in the cells 

 of Spirogyra the bodies constituting the 

 genus Pythium, and apparently connected 



