ZYGNEMACE^E. 79 



the whole evidence upon which this species is inserted. The figure in 

 the " Gleanings," as represented, in part, on our plate 29 (fig. 3c), is so 

 manifestly insufficient, without measurements, that the species is intro- 

 duced with some hesitation. The rest of our figures, and the descrip- 

 tion, are derived from Continental sources, and represent Kutzing's 

 species. 



Berkeley says of the plant he has figured : " The filaments are 

 quite unattached, and float in a rather dull green mass at the top of the 

 water, which (at least in a state of fructification) is but little mucous, 

 adhering imperfectly to paper in drying. But as the plant has only been 

 once met with, and it is well known that other species of Zygnema are 

 much less mucous in a state of fructification, it is uncertain whether 

 this is peculiar at all to the species. Articulations 4 to 6 times as long 

 as broad, at first filled with a yellowish green sporaceous mass, without 

 any marked pellucid border, with a single row in the centre of from 5 to 

 7 larger granules. The mass at length contracts, and the row of granules 

 is no longer visible. Short tubes are thrown out from the centre of the 

 joints, by which the filaments are at length connected into a more or less 

 intricate mass, and in the tubes a globular seed is formed, which swells 

 them, and is furnished with a pellucid border. In general the spora- 

 ceous matter of only one articulation passes into the tube to form the 

 seed ; nor in such case does the joint, of which the contents still appear 

 unaltered, throw out another tube. Found at Glapthorn, Northampton- 

 shire, in the spring of 1826, in watery spots of an exposed, ill-drained 

 field." 



Plate XXIX. jig. 3- #> portion of sterile thread X 400 ; b, 

 threads in conjugation X 200; c, conjugating cells and zygospores of 

 Zygnema ordinarium, after Berkeley, magnification unknown. 



B. Zygospores produced in one or other of the conjugating cells. 

 Zygnema cxuciatum. (Vauch.) 



Sterile cells equal or twice as long as broad. 



Zygospore sphserical, formed in one or other of two conjoined 

 cells. Membrane brown and scrobiculate. 



SIZE. Cells -028 mm. broad. Zygospore '04 mm. diam. 



Cleve Mon. Zygn. p. 29, t. 9, f. 1-3. Kirsch. Alg. Sehl. p. 

 126. Kutz. Tab. Phy. v. t. 17, f. 4. 



Conjugata cruciata, Vauch. Hist. Conf. p. 76, t. 7, f. 2. 



Tyndaridea cruciata, Hass. Alg. 160, t. 38, f. 1. Eng. Bot. 

 Ed. 2, t. 2512 B. Eng. Fl. v. p. 361. Mack. Hib. 231. 



Conferva bipunctata, Dillw.Conf. t. 2. Hook Fl. Scot, ii, 81. 



Zygnema bipunctatum, Johnst. Fl. Berw. ii, 256. Gray Arr. 

 i, 296. 



Zygnema Dillwyni, Kutz. Tab. Phy. v. t. 17, f. 



In ditches, pools, &c. 



The form figured by Dillwyn is more slender than the typical form 

 and is considered by some as a distinct variety. 



There is, perhaps, some difficulty in determining the exact limits of 

 the three species^, cruciatum, J5. stellinum, andJk Vaucherii, unless by 

 merging the latter two in one, and accepting Z. cruciatum as possessing 

 globose zygospores, whilst the other species has oval, or somewhat elon- 

 gated zygospores. 



Plate XXX. fig. 1. a, portion of sterile thread X 400; b, conjugat- 

 ing threads with zygospores X 200 ; c, mature zygospore X 400. 



