470 Frit &ch. — The Structure- and Development of 
has already noticed that only those plants which have a firm 
substratum, and therefore a branched basal disc, continue to 
grow and divide ; whereas those of the second type almost 
invariably form zoospores before undergoing even a single 
division. Wille (p. 456) pointed out that this is doubtless of 
Fig. 25. a , b,c,g, and n , Oedogonium capillare, Kiitz. a. Young floating plant 
with rhizoid; the contents have rounded themselves off. b. Young unicellular 
plant with a sack-shaped root-end. c. The sack-shaped root-end has grown out 
to form three long rhizoid s. g. Apex of young plant, showing two tips. 
n. Attaching-disc seen from below, d, e, f, i, j, k and /, Oedogonium spec, from 
River Severn, d. Two-celled plant with basal disc. e. Two-celled plant with 
normal type of root-end ; v = mass for attaching plant to substratum, f Empty 
unicellular plant with lid, which has returned to the position it had before libera- 
tion of the contents of the cell. i. Basal disc with upturned ends. j. Branched 
root-end. k. Unicellular plant with rhizoid ; not yet fully-developed. /. Young 
plant, whose rhizoid has firmly curled itself round another empty individual ; 
v — same as above, m. Oedogonium cardiacum , Wittr., usual type of root-end in 
floating plants; r= ring of brown matter. o,p, Oedogonium Vaucherii, Braun. 
0. Abnormal zoospore formation, p. Liberation of abnormal zoospores. ( x 415.) 
