Rivulariacece 337 



Sub-order 2. TRICHOPHORE^E. 



This is a small group containing some of the most character- 

 istic of the blue-green Algse. The trichomes are strongly attenu- 

 ated either towards one end, or from the middle towards both 

 ends, and in all cases they are sheathed. The sheaths are generally 

 strong, rarely hyaline and delicate, often lamellose, and fimbriate 

 or ocreate along their margins. In certain genera, such as in 

 Dichothrix and Ammatoidea, a false branching is present. Hetero- 

 cysts are present in some genera, but absent from others. Asexual 

 reproduction takes place by the formation of hormogones, but in 

 Gloeotrichia spores are developed from the basal cells next the 

 heterocysts. 



There are two sharply differentiated families : 



Family 1. Rivulariacece. Trichomes attenuated from the base to 

 the apex, which is piliferous ; heterocysts basal (rarely absent). 



Family 2. Camptotrichacece. Trichomes attenuated from the 

 middle towards each extremity ; heterocysts absent. 



Family 1. RIVULARIACE^E. 



Algse of this family are fairly abundant in mountainous dis- 

 tricts, and they also occur sparingly in the less elevated parts of 

 the country. They are found principally on the dripping rocks of 

 waterfalls, cataracts and streams, or at the margins of rocky lakes. 

 They form soft felt-like expanses, or hard hemispherical masses, 

 generally of a brown colour, but a few of them occur as blue-green 

 nodules attached to the stems and leaves of submerged plants. 



The trichomes are all attenuated to a hair-like point, and at 

 the broad base, in all except a few species, one or two heterocysts 

 are located. Occasionally intercalary heterocysts are present in 

 addition to the basal ones. The sheath is tubular, gelatinous or 

 membranous, and is frequently strongly lamellose. In some species 

 the lamellae of the sheath become dilated upwards, thus giving 

 the exterior of the filament a fimbriate appearance. It frequently 

 happens that the sheaths of adjacent filaments become fused to 

 such an extent that their individuality is lost. The usual colour 

 of the sheaths is yellow or yellowish-brown, and in some cases 

 they are indurated with carbonate of lime. 



The filaments exhibit a false branching due to the growth of 

 w. A. 22 



