OHARACEJE. 



333 



plant is composed of a jointed stem, which bears whorls of 

 leaves at regular intervals. The stem is one-celled in trans- 

 verse section, as in Nitella, or it has a large axial cell, which 

 is surrounded by many long narrow ones, which form a 

 cortical envelope, as in many species of Oliara. In some 

 species the stem and leaves become incrusted with lime, giv- 

 ing to them a good deal of hardness and brittleness. 



{a) The class is readily divisible into two orders — Nitelleae and 

 Charese.* 



Order Nitellese. — In this order the stem and leaves are always 

 naked — i.e., not cor- 

 ticated ; the leaves 

 are in whorls of 

 five to eight, and 

 bear large leaflets, 

 which are often 

 many - celled. The 

 sporocarps arise sin- 

 gly or in clusters in 

 the forkings of the 

 leaves, and each has 

 a crown consisting 

 of two superimposed 

 whorls of five cells 

 each. 



These delicate 

 plants occur in 

 ponds and streams, 

 and are rarely more 

 than a few centi- 

 metres in ^^^S^^- Yig.2SI9.-C/MrafragUls a, an isolated shield, m, seen 

 Two genera — Nitella from within, witii manu •riiim bearing Tlie filaments, &, in 



A m„i„.n.,nn «ro wliicli the spevraatozoids nre developed ; c, a small portion 

 ana i oiypeua — aie ^^ ^^^^ ^^ ^^^ filaments, th • fpermatozoids not shown ; A, 

 diatino-uished by the two free spermatozoids. a and 6 X 50 ; o and A X 800.— 



•i-" iii *!.„ After Thuret. 



position of the anthe- 



ridium, which is terminal upon the single node of the primary leaf in 

 the former, while in the latter it is lateral, and the primary leaf has 

 two or three nodes. 



The species of Nitella (ten to fifteen of which are American) are ar- 



* What follows is mainly from a synopsis of the Characese, furnished 

 for this work by Dr. T. F. Allen, tlie author of " Characese Americanae," 

 now issuing in numbers. Use has also been made of Dr. B. D. Hal- 

 sled's paper on the " Caasification and Description of the American 

 species of CljaracesR," published in Proc, Boston 8oc. Nat. SUt , 1879, 



