Timbcrlake — Swarm-Spores of Hydrodictyon. 495 



caused apparently by the action of the killing fluid on the chlo- 

 rophyi and the frequent distortion of the structure of the pro- 

 toplasm. Solutions containing mercuric chloride were gen- 

 eralh' unsatisfactory since nearly all details of structure were 

 lost in material killed in them. 



The best stain for delicacy of differentiation was Flemming's 

 well known triple stain, although very good results were ob- 

 tained by the use of Zimmerman's Fuchsin-Iodine green. This 

 brought out the figures of the dividing nuclei very well, but 

 was of little value to aid in studying the pyrenoids and other 

 structures. 



I have discussed in anotlier connection (29) the general 

 structure of the cell and have showed that there is no distinct 

 chromatophore in Hydrodictyon. In tliat place I pointed out 

 that the pyrenoids and nuclei were distributed in such a vray as 

 to preclude the possibility of the protoplasm between the 

 plasma and the vacuolar membranes being differentiated into 

 distinct layers. We may then, pass directly to a consideration 

 of the structure of the cytoplasm and nuclei and the process of 

 cleavage. The cytoplasm varies in appearance from an al- 

 most homogeneous finely granular mass with ang-ular vacuoles 

 placed quite wide apart, to a decidedly foamy structure whose 

 typically rounded alveolae differ much in size ranging from 

 very minute, scarcely perceptible openings to quite large vac- 

 uoles whose diameter extends nearly the w^hole depth of the 

 plasma layer. Xeither of these appearances is confined to any 

 one stage in the development of the cell. They occur in the re- 

 cently formed swarm spores as well as in the mature cell, and 

 it is quite probable that they simply represent different con- 

 ditions of metabolism, etc. The foamy appearance is however 

 much the more frequent of the two in all stages. In many cells 

 having this alveolar structure, there is a tendency for the small 

 alveoli to be arranged in rows giving the appearance of furrows 

 or tubes through the cytoplasm, but in nearly all cases strands 

 or lamellae could be detected cutting off rounded alveoli (Figs. 

 3, 21). During cleavage there is often a noticeable tendency 

 for tlie larger vacuoles to be aggregated along the cleavage fur- 

 rows (Figs. 24-26) in a manner much resembling the arrange- 

 ment in Synchitrium. 



