FILAMENTOUS THALLUS OF DUMONTIA FILIFORMIS. 443 
(4) These specialized outgrowths emerge from the creeping 
thallus—remaining attached to it by their basal portion—and by 
the subsequent growth and division of the constituent filaments 
give rise to the annual, well-known Dumontia filiformis thallus. 
EXPLANATION OF THE PLATES. 
Puate XXXV. 
Dumontia filiformis. 
Fig. 1. Creeping thallus, cr.th., in vertical sect. An early stage in the deve- 
lopment of the annual thallus is shown at a. The detached and 
disorganizing articulations of the parent filaments are seen at J. ¢, 
persistent base of annual thallus; d, attaching plug of tissue; Fs. 
Fucus serratus, trans. sect. x 100. 
2. Portion of creeping thallus illustrating exogenous mode of origin of the 
annual thallus. a, specialized rows of cells; x, a filament in very 
early stage of septation. x 300. 
3. A. Ordinary filaments of creeping thallus; s.d., commencement of 
branching. B. <A filament from an exogenous group showing early 
stage of septation, C. Another filament showing the next stage of 
septation to the preceding. 
Puate XXXVI. 
Fig. 4. A. Two filaments dividing in an intercalary manner at a' with secondary 
apical cells ap.c'.; ap.c., terminal, or apical, cell of the ordinary 
creeping thallus filament ; protoplasts only figured. B. Two 
specialized filaments from endogenous group a of fig. 1; therefore 
their apical cells, ap.c'., are secondary ; 5r., point where the specialized 
filaments branched from an older one. ©. Upper portion of two 
specialized filaments that have begun to elongate and of which the 
discoid cells have just begun to divide. x 450. 
5. Protruding group of specialized filaments, a. p./., layer of a parasite 
between the basal disc, cr.th., and the host, F.s. x 100. 
6. Young annual thallus, a, showing relation to disc, cr.th., and host, Fs. 
x 6. 
7. Lower portion of an annual thallus, a, in long. sect., showing details of 
relation to the perennial creeping thallus, cr.th. ; c, medullary fila- 
ments. X 100. 
