NOSTOC. 



543 



the slime-canal into the gland itself, and there occupy the 

 space left by the glandular cells on their conversion into slime. 

 Thence the filaments find their way into the intercellular spaces 

 of the starch-containing parenchyma surrounding the gland, and 

 become closely applied to the cell-walls. The Nostoc then bores 

 through or dissolves the cell-wall, absorbs the starch, and grows 

 vigorously till it fills the whole cell. In this manner the 

 Nostoc spreads through the cortical parenchyma of the Gunnera 

 stem from cell to cell. The stem glands in course of time 

 become inactive and the canal closes up, so that the Nostoc is 



Fig. 321. — Anabaena cycadearum. A, Coral-like surface-roots of Cycas, B, Trans- 

 verse and loDgitudinal sections of A ; the double line indicates the distribution 

 of the Nostoc. (v. Tubeuf del.) 



completely shut in. In this condition it is absolutely de- 

 pendent on nourishment derived from the host-cells, and seems 

 to thrive on it. No outward symptoms of disease can be 

 observed on Gunnera with enclosed Nostoc, the local destruction 

 of the cell-contents, the loss of starch, and the filling up of 

 the tissues with filaments of Nostoc having apparently no 

 effect. The species of Gunnera have a very short stem with 

 a growing point hardly raised above the level of the soil, so 

 that the Nostoc easily finds its way there. No algae have 

 been found in the petiole and lamina of the gigantic leaves. 

 Gunnera may easily be cultivated although it contains no 

 Nostoc. 



Jonsson ■* regards Nostoc gunnerae as identical with N. puncti- 



^Jonsson, Botan. Notiser, 1S94. 



