PICTURED-KEYS TO THE COMMON GENERA 

 OF FRESH-WATER ALGAE 



la Plants large (macroscopic), up to 40 or more cm. high, growing 

 erect, with stem-like whorled branches and iorked "leaves" clearly 

 visible to the unaided eye. Fig. 1-3 Family Characeae 2 



lb Plants microscopic, or ii macroscopic with cellular structures and 

 branches not visible to the unaided eye, or scarcely so 4 



2a Branching unsymmetrical, with dense heads oi short branches and 

 scraggly longer ones; microscopically showing globular antheridia 

 (male organs) lateral, beside the oval oogonia (female organs). 

 Fig. T TOLYPELLA 



Fig. 1. Tolypella intricata (Trentep.) v. 

 Leonh. a, Portion of plant showing 

 habit of branching; b, a node show- 

 ing four oogonia and one antheridi- 

 um; c, an oogonium showing the 

 'crown' cells; d, tip of branch. 



A rather rare plant in North America, 

 occurring in hard water lakes mostly. 

 It appears very much like Chara (Fig. 

 2) in need of a hair-cut but unlike Chora 

 it does not form dense beds in the bot- 

 tom of ponds and streams, but occurs 

 singly or in sparse clusters. Under the 

 hand lens Tolypella shows its true re- 

 lationship to Nitella (Fig. 3) in not hav- 

 ing column-like or fluting cells along 

 the stem and branches. 



Figure 1 



2b Branching symmetrical with rather evenly spaced whorls of equal- 

 length branches at nodes of the stem; antheridia above or below 

 the oogonia 3 



'Some of the illustrations used in this volume have been redrawn from figures pre- 

 viously published by the author. 



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