THE BROWN ALG& 



235 



Fig. 194- 



A group of Diatoms: c and d, top and side 

 lews of the same form; e, colony of stalked 



while others are attached to objects by gelatinous stalks, the 



stalks becoming branched as the diatoms multiply by fission. 



They possess chlorophyll, which, however, is often more or less 



obscured by brownish or yellowish pigments. In multiplication 



the protoplast divides in line with 



the plane between the two valves, 



and the two daughter cells sepa- 

 rate each with one valve. The 



naked part of the protoplast now 



deposits a new valve on that side. 



This new valve must necessarily 



fit inside of the old one. It is 



evident, therefore, that some of 



the new plants become smaller 



and smaller with each successive 



division. If these divisions con- 

 tinued, the cells would in time 



become infinitely small But they Kerner-) 



finally cast off both valves and grow to the normal size. Such a 

 cell is called an auxospore (an increasing 

 spore). A process of conjugation also takes 

 place in some species when the protoplasts 

 from two cells unite to form an auxospore. 



THE BROWN ALG^ (PH^OPHYCE^). 



380. General characters. The brown 

 algae chiefly inhabit salt water and they are 

 widely distributed along the shores of oceans 

 and seas from arctic to tropic regions. While 

 there are many small filamentous forms, 

 the class is remarkable for the number of 

 large forms exceeding in size any of the other 

 algae. In many of these the plant body is 

 itata, forma differentiated into stem and leaf-like struc- 

 tures, and the stems are attached to rocks by 



N rth Sea ' 



