EXPLAISI ATION OP THE PLATES. 257 



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PLATE X. 



Fig. la. A frond of Sirosiphon ptilvinalus, Breb., var. parvus, from a siiccimeii collect! d by 

 Dr. J. G. Hunt, near Philadtlphia. The ground color of this Bgure is too yellow. 

 F'ig. 16. A fragment of the same, magnified 400 diameters. 



Fig. 2. A row of cells of Pleurococcus scrialua, Wood, magnified 4C0 diameters. 



Fig. 3 a. A portion of the old external part of a mass of Palmclla Jessenii, Wood, magnified 7jO 

 diameters. 



Pig. 3 6. A fragment from the interior of such a mass of the same fuiii)lificatioii. 



Pig. 3 e. A portion of the soft jelly of a young actively growing mass, magnified 750 diameters. 



Fig. 4. A frond of Dictyospheerium pulchellum, Wood, magnified 4C0 diameters. I at first 

 referred this plant to the genus Botryococcus, and distributed some specimens under that generic title, 

 and so marked my original drawing. 



Pig. 5. A slice of a youngish frond of ralmrlla dura, Wood, magnified 4G0 diameters. 

 Pig. 5 6. A fragment from an old frond, showing the spores in various stages of growth. The 

 color of the large spores is not nearly dark enough, it should be much more brownish. 



PLATE XI. 



Fig. 1. Different forms of Scencsdesmus pjolymorphtis, Wood, magnified 450 diameters. 

 Pig. 2. Scenedesvuis quadricauda, Breb., magnified T50 diameters. 

 Pig. 3. Scenedesmus rotundatus, Wood, magnified 750 diameters. 



Fig. '4. Ordinary vegetative cells of Palmogla'a clep)sydra, Wood, in different stages or con- 

 ditions of life-history, magnified 750 diameters. Those cells which have the endochrome much 

 l)roken up are believed to be preparing for conjugation. 



Fig. 4 a. A pair of cells uniting in conjugation. 



Pig. 4 b. Cells which have united so that the young spore is very apparent wiih the empty seiui- 

 cells of the parents attached to it. 



Fig. 4 c. A more advanced spore and empty semi-cells. 



Pigs. 4 d and 4 e. Matured or nearly matured spores, as seen with diflVrcnt focussing; in the 

 first the upper surface of the spore is especially brought out. All these figures, e.\ccpt 4 6, are 

 magnified 750 diameters. 



Figs. 5 and 5 o. Different forms of Clusleriurn acerosum (Schr.), magnified 250 diameters. 



Fig. 5 6. Empty conjugating cells with nearly matured spore. 



Pig. 6. Outline of Closterium areolatum. Wood, magnified IGO diameters. 

 Pig. G a. End of a dead, empty frond, enlarged 1375 diameters. 



Fig. 7. Outline of Closterium Venus, Ktz., magnified 450 diameters. 

 (These last three species are incorrectly labelled on the plate, Cosmarium.) 



PLATE XT I. 



Fig. 1. Closterium I inrafum, 'Ehvh. (Incorrectly labelled on the plate Cosmarium.) Afagni- 

 fied IGO diameters. 



Fig. 2. Closterium Uhrenbergii, Menegh., magnified IGO diameters. 



Fig. 3. Closterium roslratum, Ehrb., magnified 260 diameters. 



Fig. 4. Closterium Diamf, Ehrb., magnified 2G0 diameters. 



Fig. 5. Closterium pnrvulum, Na^g., magnified 450 diameters. 

 33 October. 1872. 



