154 INTRODUCTION TO CEYPTOGAMIC BOTANY. 



fact which soon attracts attention in germination by the occur- 

 rence, in a spiral direction, of linear tracts free from endo- 

 chrome, which soon unite with each other so as to be con- 

 tinuous, and to divide the endochrome into a distinct spiral 

 band. 



127. The species are, with scarcely an exception, inhabitants 

 of fresh water, and are probably widely distributed. Nume- 

 rous species occur in the collections of Dr. Hooker and Dr. 

 Thomson, both in the more northern and southern Himalayas, 

 but they descend into the lower parts of India, as at Bijnour 

 or in Silhet. The curious genus Thwaitesia first occurred in 

 Algiers ; but there is a species also in the Soane river, in which 

 not only are there tetraspores, but the endochrome is in some 

 instances resolved into active molecules. The spores are formed 

 indifferently in the joints and conjugating tubes. The most 

 striking feature, indeed, amongst the fresh water Algae of 

 India, is the prevalence of Zygnema and Tyndaridea, which 

 occur under a variety of forms, and sometimes with very thick 

 gelatinous coats, to which a parallel is afforded by the beau- 

 tiful species Tyndaridea anomala, figured by Mr. Ralfs, 

 Eng. Bot., Supp. t. 2899. The genus Zygnernxi ascends as 

 high as 15,000 feet in the Himalayas, while Oscillatoria, 

 Gcenocoleus, and Conferva reach 17,000, or even 18,000 feet. 

 One very interesting form mentioned above, either belonging 

 to the genus Zygnema, or possibly constituting a distinct genus, 

 occurs in streams at 5,000 feet in Sikkim, consisting of highly 

 gelatinous threads of the normal structure of Zygnema, but 

 forming a reticulate mass. The threads adhere to each other 

 laterally, and the articulations are very long, and contain only 

 a single spiral band. Amongst these are the normal threads 

 of some Tyndaridea. They do not appear to be common in 

 the southern hemisphere. No species occurs in the Flora 

 Antarctica ; Tyndaridea anomala, and one other species only, 

 have been found in New Zealand. Montagne's Sylloge, in 

 addition to Thwaitesia, contains but a single extra-European 

 species from Cayenne ; besides which, there is scarcely more 

 than a trace of them in South America. 



128. A most singular Alga occun-ed amongst the Himalayan 



