136 BOTANY. 



whole net is a colony of plants, each of which reproduces 

 by the formation of zoospores : the latter after a time ar- 

 range themselves in the form of a net. New colonies are 

 formed, also directly by the protoplasm of a cell first break- 

 ing up into a great number of small ones (by internal 

 cell-formation), these soon arrangeing themselves into a 

 miniature net inside of the old cell-wall. The old wall 

 eventually decays and sets free the new colony. 



241. The Pond-scum Parasites. — There are many para- 

 sitic Green Slimes (of the family OhytridiaccEe) which live 

 in the cells of plants and animals. They are minute 

 chlorophyll-less cells, which eventually break up into 

 zoospores. They are common in cells of pond-scums 

 (Spirogyra, etc.), diatoms, desmids, and other aquatic 

 plants. A few species of the Gall-fungi (Synchytrium) oc- 

 cur in the aerial leaves of higher plants, forming rust-like 

 spots, consisting of cells from which zoospores will eventu- 

 ally escape. 



Practical Studies. — (a) Scrape off a little of the green, paint-like 

 coating from a flower-pot, a damp wall, or a sidewalk plank, and ex- 

 amine under a high power for common Green Slime (Protococcus, 

 etc. ). 



(J) Examine the green plants collected from ponds and ditches for 

 Scenedesmus and Pediastrum. The former may often be found in 

 great numbers on the sides of glass jars or aquaria containing pond- 

 plants. 



(c) In midsummer search quiet pools for water-nets. With a fine 

 scissors cut out a piece of one and mount carefully in water. Study 

 with a low power of the microscope. Some of the cells will be found 

 producing zo5spores. Search for young nets forming within the old 

 cells. 



(d) Carefully examine the cells of pond-scums, diatoms, desmids, 

 etc., for Pond-scum Parasites (Chytridiacese). They may be recog- 

 nized as spherical or flask-shaped colorless bodies within the cells. 

 They are usually most abuildant in water which has been standing 

 for some time. 



(e) Gall-fungi may be found upon the leaves of Evening Primroses, 



