94 ZYGOI-HYCE.E. 



rated by distinctions so minute and variable, that they cannot be main- 

 tained as other than varieties, and Zyynema mcilleolwn and Z. affine were 

 at the time suspected of being varieties the one of the other. 



Plate XXXVII. fig, 1. Variety gracilis. a, sterile cells X 200 ; fc, 

 conjugating cells with zygospores X 200 ; c, fertile cells of Rhyncho- 

 nema form with zygospores X 200 ; d, ontliue zygospores X 400. Fig. 2, 

 variety flavescens. a, sterile cells X 200 ; b, c, conjugating cells with 

 zygospores X 200; d, fertile cells of Rlninclionema form with zygospores 

 X 200 ; e, outline zygospores X 400. Fig. 3. variety parva. a, sterile 

 cells x 200 ; b, conjugating cells with zygospores X 200 ; c, outline 

 zygospores X 400. 



SECTION 2. Cells replicate at tlieends. 



A. Chlorophyll bands usually two or more. 

 Spirogyra insignis. Hass. 



Sterile cells with the extremities replicate, 41 to 5 (rarely 6) 

 times as long as broad, chlorophyll bands 2 to 3, lax, with 1 to 2 

 turns of spiral, or nearly erect. 



Spores ovate-elliptic, twice as long as broad, membrane even/ 



Sporiferovts cells slightly swollen. 



SIZE. Sterile cells -03--035 mm. Zygospore '04--05 mm., 

 2 to 3 times as long. 



Rabh. Alg. Eur. iii. 243. 



Zygnema insigne, Hass. Alg. 440, t. 103, f. 1,2. 



ZygnemaHassallii, Hass. Alg. 157, t. 36, f. 4,5. Jenner Fl. 

 Tunb. Wells, 182. 



Spirogyra insignis, Kutz. Tab. v. t. 31, f. 4. Sur. Obs. 

 t. 1, f. a. 



Rhynchonema HassaUii, Kutz. Tab. v. t. 32, f. 7. 



Spirogyra Braunii, Rabh. Alg. Ex. No. 1310, 1395. 



Spirogyra Hantschii, Eabh. Alg. Ex. No. 1291. 



Spirogyra Theobaldii, Kutz. Tab. v. t. 31, f. 2. 



Spirogyra Hassallii, Petit Bull. Soc. Bot. Fr.; Spirogyra t. 2, 

 f. 6-8. 



Rhynchonema gallicum, Ripart. in Petit Spirogyra. 



In streams. 



The number of British species in which the cells have replicate ends 

 is much less than of those with truncate ends. We have only included 

 two species with two or more chlorophyll bands, in one of which the 

 membrane of the zygospore is smooth, and in the other punctate. Doubt- 

 less neither of them are common. 



Plate XXXVIII. jig. 1. o, c?, sterile cells X 200 ; &, conjugating cells 

 with zygospores X '200 ; c, fertile cells of Rhynchonema form X 200; 

 outline zj-gospore X 400. 



Spirogyra calospora. Cleve Jfon. Zyg. p. 26, t. 8,/. 1-5. 



Sterile cells with the extremities replicate, 6 to 12 times as long 

 as broad, chlorophyll bands 1 to 3, making 2 to 7 turns. 



Spores elongate, obtuse ovoid, 1 J to 2 times as long as broad, 

 membrnne yellow, screbiculate. 



Sporiferous cells scarcely turgid. 



