54: 



ATHOGENIC ALGAE. 



naked eye by bluish-green spots 

 rhizomes of the host (Fig. 319). 



sections of stems and 



Fig. 319.— Xosloc gunnerae. Lone;i- 

 tudiual section through the apex of a 

 stem of Giitinera manicala. The punc- 

 tated spots indicate the position of 

 J\'r)s(oc-colonies. (v. Tubeuf del.) 



the remaining glandular 

 into the same substance. 



These originate as follows : the 

 species of Guniura possess charac- 

 teristic mucilage-secreting organs, in 

 the form of fissures of the leaf-tip, 

 collaters on the leaves, and glands 

 on the stems. Merker^ found that 

 these glands originated endogenously 

 in the growing point between each 

 pair of leaves. The mature glands 

 are covered only by the epidermis, 

 and when activity commences the 

 uppermost cells of the gland- tip, 

 after swelling, become detached and 

 converted into slime (Fig. 320). 

 Ultimately the epidermis is ruptured 

 by the pressure of the slime, and 

 cells are in turn rapidly transformed 



Fig. 320. — No.itoc gunnerae. Longitudinal sections through a gland in stem of 

 Ounnera macrophylla. c, Epidei'mis ; ■■<, slime-canal ; no, colony of Nostoc. 

 (After Marker.) 



The Nostoc finds its way into the gland as soon as the 

 epidermis is broken, apparently attracted there by some 

 secretion. Merker found that the Nostoc filaments pass down 



^ Merker, " Gimnera macrophy/la ," Inaugural Dissertation, 1888. 



