134 THE PLANTS 



families are equally interesting from similar or different 

 points of view. Therefore collectors of algae who are 

 not botanists may feel sure that they can render good 

 service to science if they will only collect carefully, as 

 only well-prepared and duly labelled collections are of 

 value. 



The Myxophyceae, or blue-green algae, are small, and 

 the least organized of the algal tribe ; they are either 

 uni- or multi-cellular. The latter form long filaments 

 enclosed in a common cell-sheath, and dividing, for 

 the sake of reproduction, into several portions called 

 " hormogonia," which move out of the sheath. The 

 young hormogonia secrete a new cell-sheath, and 

 develop by division of their cells into a new filament. 

 Myxophyceae, after having been collected, should, as 

 soon as possible, be spread out on the paper on which 

 they are to dry, and not left to stand overnight. If 

 this is neglected, the hormogonia will, in all probability, 

 have moved out from the sheaths, and the specimen 

 will be worthless. 



Myxophyceae live, as a rule, in the upper littoral 

 zone, attached to stones, pebbles, or other algae. 

 Lyngbya majuscula — the mermaid's hair — is some- 

 times found floating on the sea. Some species of Calo- 

 thrix (Fig. 47) form patches on the rocks ; species of 

 Rivularia have a hemispherical thallus, either solid, 

 from as big as a pin's head to J inch in diameter, or 

 hollow and forming soft expansions. Sometimes 

 Scytonema and Lyngbya will cover the rocks with a 

 slippery coating, disagreeable, and even dangerous to 

 the collector when the waves are strong. Myxophyceae 

 are found in all temperate and tropical seas ; their 

 genera and species have, as a rule, a very wide distri- 

 bution. In the Arctic and Antarctic they seem to be 

 rare. 



