ALGAE. SI PHONE AE. 



2 9 



4. Confervoideae. Thallus of cell-filaments or cell-surfaces. Asexual organs of 

 propagation occur in all species in the shape of zoospores, which are formed either on 

 the thallus or only after the germination of the sexually produced spores (Sphaeroplea). 

 The Conjugatae and Characeae are connected with the Confervoideae, as collateral series 

 of forms which have no zoospores. 



1. SIPHONEAE . 



The Siphoneae or Coeloblastae form a rather large group of Algae which are 

 for the most part marine, and which, with all the differences of habit of the several 

 species, have this character in common, that no septa as a rule appear in the 

 tubes of which they are composed, except in the formation of organs of re- 

 production. Hence the vegetative body of these 

 plants, which often attains to a considerable size, 

 is not divided into single cells, but its cavity is 

 continuous; and Sachs calls them therefore 

 non-cellular plants growing without division 

 into compartments, while others regard them 

 for the same reason as unicellular. Numerous 

 small nuclei 2 are always present in the pro- 

 toplasmic lining of the cells, but this is a 

 peculiarity which is by no means confined to 

 the Siphoneae among the Algae. Asexual multi- 

 plication, in the species which have any form 

 of it, is effected either by swarm-spores as in 

 Botrydium and some species of Vaucheria, or by 

 motionless cells as in other species of Vaucheria, 

 while Acetabularia and a few species again of 

 Vaucheria &c. have no asexual multiplication. 

 The remarkable genus Caulerpa has neither 

 sexual nor asexual reproduction so far as is 

 at present known ; it multiplies by separation 

 of new shoots which form on the old plants. 



The simplest structure of the vegetative 

 body is found in Botrydium, a plant not un- 

 common on moist mud in ditches, &c. One 

 portion grows above ground, the other beneath 

 it. The former has the appearance of a green bladder, one to two millimetres in 

 breadth, which grows narrower downwards till it passes into the rooting-portion, which 

 is fixed in the ground and has an irregularly dichotomous branching- system. The 

 genus Vaucheria has a similar but less largely developed rooting-portion ; but the 

 upper green portion of the thallus consists of variously branched filaments, often 



FIG. 12. Botrydium granulatuni, an isolated young 

 plant, magn. 30 times ; iu root system. After Woronln. 



1 Nageli, Neuere Algensysteme, p. 58; also Caulerpa prolifera in Nageli u. Schleiden, Zeitschr. 

 f. wiss. Bot. 1844, Heft i. 



2 Schmitz, Ueber d. Zellkerne d. Thallophyten (niederrh. Ges. 7 Juni, 1880, p. 7 of the reprint). 

 Strasbnrger, Zellbildung u. Zelltheilnng, 3 Aufl. p. 65. 



