MICROSCOPIC FOKMS OF VEGETABLE LIFE. 



24:7 



divides into numerous segments (as at 1} and c), which at first are seen to 

 lie in close contact within the cell that contains them, then begin to ex- 

 hibit a kind of restless motion, and at last pass forth through an aperture 

 in the cell-wall, acquire four or more flagella (d), and swim freely 

 through the water for some time. At last, however, they come to res 

 attach themselves to some fixed point, 

 and begin to grow into clusters or 

 filaments (e), in the manner already 

 described. The walls of the cells 

 which have thus discharged their en- 

 dochrome, remain as colorless spots 

 on the frond; sometimes these are 

 intermingled with the portions still 

 vegetating in the usual mode; but 

 sometimes the whole endochrome of 

 one portion of the frond may thus 

 escape in the form of zoospores, thus 

 leaving behind it nothing but a white 

 flaccid membrane. If the Micro- 

 scopist who meets with a frond of an 

 Ulva in this condition should ex- 

 amine the line of separation between 

 its green and its colored portions, 

 he may not improbably meet with 

 cells in the very act of discharging 

 their zoospores, which 6 swarm ' 

 around their points of exit very much 

 in the manner that Animalcules are 

 often seen to do around particular 

 spots of the field of view, and which 

 might easily be taken for true Infu- 

 soria; but on carrying his observations 

 further, he would see that similar 

 bodies are moving ivithin cells a little 

 more remote from the dividing line, 

 and that, a little farther still, they are obviously but masses of endochrome 

 in the act of subdivision. 1 Of the true Generative process in the Ulvaceee, 

 nothing whatever is known. 



246. The Oscillatoriacece constitute another tribe of Protophytes of 

 great interest to the Microscopist, on account both of the extreme sim- 

 plicity of their structure, and of the peculiar Animal-like movements 

 which they exhibit. They are continuous tubular filaments, formed by 

 the elongation of their primordial cells, usually lying together in bundles 

 or in strata, sometimes quite free, and sometimes invested by gelatinous 

 sheaths. The cellulose envelope (Fig. 146, A, a, a) usually exhibits some 

 degree of transverse striation, as if the tube were undergoing division 

 into cells; but this division is never perfected by the formation of com- 

 plete partitions, though the endochrome shows a disposition to separate 

 into regular segments (B, c), especially when treated with re-agents. 



Successive stages of development of Ulva. 



1 Such an observation the Author had the good fortune to make in the year 

 1842, when the emission of zoospores from the Ulvaceee, although it had been de- 

 scribed by the Swedish Algologist Agardh had not been seen (he believes) by any 

 British naturalist. 



