6 M. G. Thuret on the Reproduction of certain Nostochinese. 



found surrounded by a few irregular mucous filaments. These 

 filaments (cils), the presence of which is very common on the 

 heterocysts of Anabaina, are probably nothing more than para- 

 sitic productions. 



After the formation of the heterocyst, the sporange is very 

 soon developed at the expense of the next joint. This becomes 

 elongated, enlarged, and its contents become very granulose. 

 By degrees its walls become thickened, and assume a brown 

 colour. It is not, as Mr. Ralfs states, the substance contained 

 in the sporange which takes this colour; it is merely the wall of 

 the cell. The interior of the sporange is filled up by an elliptical 

 spore, which may be distinguishable through the transparency 

 of the sporange, and which preserves the green colour, as may 

 be easily ascertained by causing it to emerge from the sporange 

 by slight pressure. Filaments are often met with terminated at 

 both ends by a heterocyst. It is more rare to see one filament 

 bearing a sporange at each extremity, and in such cases it has 

 always appeared to me that the development of one of the spo- 

 ranges has preceded that of the other (fig. 9). 



M. Fischer, in the memoir above cited, mentions an observa- 

 tion of M. Nageli on the germination of Cylindrospermum*. 

 The description which he gives, besides being very short and 

 incomplete, does not appear to agree with what I have seen my- 

 self in these plants. 



The first species in which I observed the reproduction is re- 

 markable from the rugose surfaces of its sporanges. The fila- 

 ments are about j^q to -g-oVo^ °^ an mc ^ * n diameter. It is 

 the same plant that has been published in the 'Fasciculi' of 

 M. Rabenhorstt under the name of Cylindrospermum majus, 

 Kutz. It is possible that it may be really the species thus 

 named in the ' Species Algarum ;' but I cannot affirm anything 

 on that point; for M. Kiitzing does not mention the rugose 

 aspect of the sporanges, and the ( Tabulse Phycologicse' of the 

 same author are unfortunately far from supplying the deficien- 

 cies of his diagnoses. 



I found this species, in the month of June of last year, float- 

 ing in a ditch in mucilaginous masses. The sporanges were 

 abundant, of a brown colour, and appeared perfectly ripe. This 

 circumstance induced me to place some fragments of the plant 

 in a drop of water upon slips of glass, keeping them under a 



* " In Cylindrospermum, Prof. Nageli has actually observed the germina- 

 tion. After a longish stage of rest, a repeated division suddenly occurs in 

 the cells ; the outer thick wall is dissolved, and the young filament com- 

 mences its growth by simultaneous division of all its cells." — Fischer, I. c. 



P. 7. 



t Die Algen Sachsens, no. 411. 



