CI.OSTEISIUM. 39 



have a firm cytiodemi and retain their outline when dry or 

 empty ; others, not striated are more flexible and collapse when 

 dried. The chlorophyl escapes by a slight separation of the 

 semi-cells, and leaves the case colorless. 



Faded specimens of the striated forms are best adapted for 

 examination ; the striae, barely discernible in green condition, 

 become distinct ; the cases flatten somewhat in drying, the 

 breadth in center increases and the ends appear more attenu- 

 ated, hence some allowance should be made in describing them. 



Conjugation takes place by a process which appears the same 

 as in other conjugate. Two cells drawn into close proximity, 

 put forth small tubular prominences by which they unite, the 

 chlorophj'llous cytioplasm of the two cells concentrates at their 

 1 unction, in the connecting tube; this enlarges more and more 

 until the whole of the contents of the two cells are commingled, 

 and condense into a seed-like mass. This becomes smooth, 

 spherical, sometimes quadrangular, and is known as the zygo- 

 spore. Compare Plate IX. The coupling usually takes place 

 from the concave sides, but not universally ; have found them 

 united from the convex sides also. 



SECTION 1. Cells more or less cylindrical, slightly bent, ends scarcely, or not at 

 all tapering; zygospores orbicular or square 



C. OBTUSUM. Breb. Plate VII, fig. 1. 



Cylindrical, lightly curved. 5-10 times longer than broad, 

 ends not tapering, broadly rounded, cytioderm colorless and 

 smooth. 



Diameter 5-11 /^. 



Often in gelatinous masses on planks, on the sides of flumes. 

 Pennsylvania. 



C. JUNCIDUM, Ealfs. Plate VII, figs. 2, 3. 



Cells long cylindrical, somewhat curved and tapering 

 towards the ends; 20-30 times longer than broad, apices 

 obtusely rounded; vacuole small and indistinct. 



Diameter 11-12 p.. 



Variable in thickness and length ; occurs frequently in 

 ponds from Maine to Florida. 



. JUNCIDUM, forma GRACILLIMA-LAEVISSIMA, Breb. Plate VI, 



fig. 21. 



Very much smaller than the type-form and destitute of 

 striae. 



Frequent in ponds near Maitland, Florida. 



