THALLOGENS. 9 



A deposit near Monterey, Cal., is 50 feet thick, white and fine as chalk. 

 A deposit in Bilin, Bohemia, is 14 feet thick. Its material was the 

 first used as Tripoli, or Rotten-Stone. 



Sub-Tribe 2. Desmidiacese. — Like Diatoms, but green and not sili- 

 cious. Many genera; fresh water. 1. Pediistrum, cells in families 

 in a flat, thalloid mass ; many species. P. gramddtum, zoospore, Pig. 

 11, E. 2. Closterium acutum, Pig. 13, B, C, D. 3. Desmidium, 

 many species. 



Sub-Tribe 3. Zygnemaceae. — Green ; cells cylindric, making un- 

 branched filaments elongating (as in Bacteria) by transverse fission of 

 the cell ; cells ccmjugating with cells of other (parallel) filaments. 

 Felted masses in ditches and streams. 1. Zygnfema insigne ; 2, Spi- 

 rogyra longdta ; 3. Mesocdrpus scaldris ; all common. 



Tribe 2. Vaucheriaceae. — Internal cell-division (single zoospore 

 expelled from mother-cell). Fertilization; fls. |^. Green ; cell single, 

 in simple or branched filaments, matted in fresh water, damp earth. 

 1. VaucheriasessJiJs, Fig. 1, A, B, C, E. 2. Caulerpa, cell branched 

 and anastomosing ; sand, shaded rocks, deep water 3. Caulerpites 

 ca^itmdes, fossil ; Silurian. 4. Halimeda, cell similar to 2 and 3, Cactus- 

 like ; H. Opuntia ; in sand and shells, tropical shores of Atlantic, Pa- 

 cific ; Mediterranean and Bed Seas. 5. Saprolegnia ; 6. Achlya ; 7. 

 Pythium ; genera resembling Vaucheria except that they ai-e without 

 chlorophyl, and are saprophytes, — parasites on dead flies, fish, etc., in 

 water. For Saprolegnia /eraa;, see Lesson XXXII., 412. 



Tribe 3. Chlorospermae. Gkeen Seaweeds. — Reproduction of 

 Tribe 2. Green ; cells simple or branched, variously arranged ; ma- 

 rine or fluviatile. Many genera. 1. CEdogonium cilidium, filamen- 

 tous; ponds. Zoo.spore, Fig. 1, D, P. 2. Acetabularia merfiier-ranea, 

 small ; cell radiately arranged on a tall pedicel ; umbrella-like, hand- 

 some ; Mediterranean. 3. Bryopsis plumbsa, cell branching, small; 

 marine, common. Fig. 15. 4. Hydrodictyon utriculdtum, Water- 

 Net ; cells forming a purse-like net. 5. Conferva, green filaments, 

 swollen with gas-bubbles as if boiling, whence the name. Several 

 species. 4 and 5 form the green scum on ponds. Confervites, fossil 

 in Jurassic and Tertiary. 



Tribe 4. Melanospermse. Olive Seaweeds. — Cell-division. 

 Fertilization. Brown or olive; various in form ; marine. 2 Sections : 



Section 1. Tangles. — Cell-division ; sori superficial. Many gen- 

 era. 1. Padina Favbnia, Peacock Laver, T high ; temperate seas. 

 Frontispiece, A. 2. Dictyota dichotoma, British coast. Fig. 16, 2. 

 3. Nereocystis ; 4. Macrocystis, Sea-Bladder, several species ; 

 cord-like, 250° to 1700° long, a bladder at apex 7° long with leaf-like 

 appendages; North Pacific. 5. Alaria esculenta, Badderlocks 

 (Baldbrlocks) ; 3° to 20° long; edible; eaten raw. British coast. 

 Fig. 16, 1. 6. Chorda /U«m, Dbad-Man's-Rope; cord-like, 20° to 

 50° long. British bays. Terror to swimmers. Palaeochorda minor, 

 fossil. Lower Silurian. Fig. 83, A. 7. Laminaria, Sba-Oar; long, 

 oar-like. Many species ; edible ; common. Laminarites, fossil, Silu- 

 rian. 8. Lessdnia /Mscescens, Sea-Willow ; 12° high, with branch- 

 ing drooping crown ; making submarine forests. S. Pacific. 



Section 2. Varecks, Wracks. — Fertilization ; fls. ^ ; jf and $ in 

 separate conceptacles. 1. Himanthalia Ibrea, Sba-Thong. Frond 

 small, cup-shaped ; conceptacles long, strap-shaped. West coast of 



