THE GREEN ALG 481 
a woolly mat which suggests the name wool-weeds as appro- 
priate for the group. A differentiation of the plant-body 
appears in a specialization of the lowest cell as an organ: of 
attachment. This, therefore, is analogous to a root while 
the remaining green part has the function of a shoot. But 
Fic. 313.—Wool-weed (Ulothrix zonata, Wool-weed Family, Ulotrichacee). 
A, young plant with basal cell (r) serving as a root-like organ of at- 
tachment, #25. 8B, part of plant with escaping swarm-spores. C, single 
swarm-spore. D, formation and escape of gametes. FH, free-swimming 
gametes. F, gametes conjugating. G, conjugation complete. 4H, zy- 
gote. J, zygospore after a period of rest. AK, zygospore after division of 
its protoplast into swarm-spores. B-K, 382. (Dodel-Port.)— 
Abundant on submerged rocks, especially in fresh water. 
the resemblance not being one of homology, it will be most 
accurate for us to name organs of this kind pseudo-roots and 
pseudo-shoots respectively. Thallus‘ is a general term for 
any plant-body in which true roots, true stems, and true 
leaves do not appear. The pseudo-shoot of a wool-weed 
elongates by fission of its cells, each of which contains a 
1 Thal’lus < Gr. thallos, a young shoot. 
