THE BROWN ALfJAL 



257 



Fig. 204- 



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 r valve must necessarily 

 fit inside of the old one. It is 

 evident, therefore, that some of 

 the new plants become smaller 



T 11 , i i . A group of Diatoms: c and d, top and side 



and Smaller With each SUCCeSSlVe view s of the same form; e, colony of stalked 

 j. T r -u j* forms attached to an alga;/ and g, top and 



division. If these divisions COn- side views of the form shown It e-,h : a 

 ,. i ,v 11 11 A - colony; i, a colony, the top and side view 



tinued, the Cells WOUld in time s hown at *, forming auxo-spores. (After 



become infinitely small. But they Kernen) 



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^). 



394. 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 cf 

 large forms exceeding in size any of the other 

 algae. In many of these the plant body is 

 forma differentiated into stem and leaf-like struc- 

 Sea ' tures, and the stems are attached to rocks by 



