1892.] THE MICEOSCOPE. 121 



many in some stages of their development present motile forms 

 endowed with such rapid motion that by the earlier observers 

 they were considered animals. Other forms constantly present a 

 motion of an oscillating or weaving nature that is absolutely in- 

 explicable to scientists, as are also the apparently intelligent 

 movements of the diatoms. 



Our knowledge of the Algfe is so incom2:)lete that the matter 

 of classification is very, difficult. One quite satisfactory division 

 makes seven orders, viz : 



Cyanophyceae. — Including the well-known nostoc and the 

 various forms of oscillaria, a form which propagates by cell di- 

 vision, and which is often found in hot springs possessing a tem- 

 perature of 115 deg. Fahrenheit. 



Protococcaceae. — The best-known species being the proto- 

 coccus nivalis, or red s7iozv^ often found in Arctic regions. 



Conjugatse. — This is one of the largest and most thoroughly 

 studied of the orders, and includes the diatoms. Desmids and 

 many filamentous forms, all, however, presenting this peculiarity, 

 inferred in the name, that the union of the contents of two sep- 

 arate and distinct cells is necessary for the production of the zygo- 

 spores or "winter" cells, the form in which the life is main- 

 tained through the season when growth is impossible. 



Volvocaceae. — The volvox globator^ the most prominent spe- 

 cies of this order, is perhaps the most beautiful and interesting 

 of all the Algae, exhibiting, as it does, a transparent ciliated 

 globe, rolling about with a dignified motion and containing 

 within many zygospores and zoospores, which, upon the bursting 

 of the parent envelop, sail away as free individuals. This spe- 

 cies w^as found a few months ago in Mountain Lake by G. O. 

 Mitchell, one of the members. 



Siphoneae. — This order presents but few fresh-water species, 

 the rare vauchcria being foimd in several pools in the Presidio. 



Confervoidese. — This order is composed largely of filamentous 

 forms which grow attached to stones, other vegetable matter, or 

 even to animals. It forms the unwelcome green coating that 

 forms upon the glass in our aquaria. 



Floridise. — This last order is the most seldom found, and is rep- 

 resented by two species. It differs from the other forms in general, 

 being of a red or purple color, instead of the traditional green. 



After thus outlining the classification, the essayist gave a de- 

 tailed account of the forms of conjugation displayed by Spirogyra^ 

 and traced the life-history of this form. The value of this class of 

 plants in the economy of nature is incalculable. Presenting to the 

 eye, as many do, the appearance of a mass of green slime, they 

 are, under the influence of the sun's rays, the most active purifiers 

 of the water, evolving large quantities of oxygen to burn up the 

 dead animal matter and to give support to the living. 



