30 THE FLORA OF NEBRASKA. 



SYNOPSIS.* 



Fam.— Pal mellaceae.— Chlorophyll-green, vegetative cells solitary or aggregated 

 in families, destitute of cilia, immobile; propagation by cell division; re- 

 production by the copulation of microzoogonidia. 



Fam— Chytridiaceae.— Unicellular parasites or saprophytes; reproduction by 

 swarm-spores and resting-spores; sexual reproduction only found in a 

 few forms; difference between antherid and oogone scarcely marked. 



Family.— PALMELLACEAE. 



Thallus one or apparently many celled; cells associated in families; the chlorophyll- 

 green of the cells sometimes changed to a reddish or purple color with age; propagation 

 by neutral zoogonidia or by cell division, rarely by granules. 



SYNOPSIS. 



A. Cells single or loosely united; never forming a colony of definite form. 

 Protococcus— Cells spherical or slightly angular, single or irregularly united. 

 Tetraspora— Cells very small, spherical, arranged in fours. 

 Characium— Single celled; epiphytic on algae and other water plants. 

 Tetraedon.— Cells, 3-many angled. 



Raphidium — Cells solitary or clustered, needle-shaped or filiform. 



B. Cells forming a colony of definite form. 



Pediastrum— Cells 3-many angled or laciniate; colony disciform. 

 Sorastrum— Cells wedge-shaped; apex bifid or emarginate, colony globose. 

 Scenedesmus— Cells elliptical, acuminate, 2-16 in a simple series. 

 Hydrodictyon.— Cells loosely united by their ends into an irregular network. 



1. PROTOCOCCUS AG. Systema Algarum 13. 1824. 



Cells globose, solitary or aggregated, membrane slender, cell contents green, 



in some species obscured or changed to red; propagation by division of 



the cell contents into zoogonidia, or rarely by simultaneous division of 



the mother-cells into daughter-cells. 

 Etymology: Greek irpurog, first, and kokkoq, berry. 

 Many of the so-called species are only spores or arrested conditions of some 



of the higher Chlorophyceae but until their position is better known they 



may be placed here provisionally. 



Protococcus viridis Ag. Systema Algarum 13. 1824. 



Thallus thin, pulverulent, yellow or obscure green, occasionally blood-red, 



often broadly expanded; cells globose, 2-3 to even 25 //; solitary or 2-4 



aggregated, cell membrane thin or occasionally broadly expanded, 



hyaline. 

 Common almost everywhere, especially in damp localities forming a coating 



on trees, rocks, old fences, etc., and even in the water among other algae- 



PI. IV., Fig. 11. 

 Under this name are included a number of polymorphous forms which are 



only arrested conditions of other algae, many of which when placed under 



proper conditions will produce the perfect plant. 

 Of the numerous described varieties we recognize only one— Var. miniatns. 



Kuetz. (including Porphyridium cruentum Naeg.). 



•The Volvocaceae, including Volvox, Pandorina, etc., were formerly included in this order, but recent in. 

 restigations indicate that their relationship is with the animal rather than the vegetable kingdom. 



