26o Phillips on a Comparative Study of the 



the depth of the drop, which would carry the plant beyond 

 the focal distance of the objective. At least this has been 

 the difficulty experienced in trying to follow Zukal's obser- 

 vations on living material in the present investigation. 



Nadson's work (57) was principally performed upon 

 Merismopedia elegans, Gloeocapsa polydcrmatica, Lyngbya 

 curvata, Oscillaria (several undetermined species), Aphano- 

 capsa Grevillei, Chroococciis turgidiis, Tolypothrix ccga- 

 grophila, Aphanizomcnon flos aquae, and for comparison, 

 the bacteria Clostridium butyricum and Cladoihrix dicho- 

 toma. For the purpose of fixation he found iodine-alcohol 

 the most useful, also a saturated aqueous solution of corro- 

 sive sublimate. Hjematoxylin was his chief stain, though 

 vesuvin, iodine green, a mixture of methyl blue and fuchsin, 

 and acid carmine were also used. Intra-vitam staining 

 with methyl blue was also productive of good results. Most 

 of his conclusions on fixed material he was able to verify 

 on living specimens, thus obviating the possibility of mis- 

 taking artifacts for normal structures. Micro-chemical reac- 

 tions did not give him any definite results and were there- 

 fore discarded. A colorless, amoeboid central body, occupy- 

 ing most of the cell, was found, distinguished peripherally 

 by phycochrome from a colorless outer layer, though this 

 latter was not to be regarded as a chromatophore, but rather 

 as protoplasm. In one form {Aphanizomcnon) vacuoles 

 were found between the central body and the protoplasm. 

 The cytoplasm had a vesiculated structure like the "waben- 

 bau" of Biitschli, and the chlorophyll and phycocyan were 

 contained in the walls of these vesicles. The central bodies 

 were not always surrounded by the protoplasm, but in some 

 filamentous forms {Tolypothrix, Aphanizomcnon) they 

 reached from end wall to end wall, thus forming a longi- 

 tudinal band along a row of cells. The central body had 

 the same vesiculated structure as the protoplasm, but was 

 not so well defined, the vesicles being filled with a peculiar, 

 deeply staining substance which the author called 'Tilling 



