92 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



zoosporangia or male and female gametangia. In the 

 former ease a short exit tube grows out from the 

 neck of the thallus (fig. 4), and as the protoplasm 

 begins to move out its tip gradually enlarges into a 

 spherical vesicle into which the entire contents of 

 the thallus emerges (figs. 5-6). Vanterpool and 

 Ledingham regarded this vesicle as the sporangium 

 proper and referred to the thallus which gives rise 

 to it as a presporangium. The emerged mass of pro- 

 toplasm soon begins to cleave progressively into 

 segments (fig. 7), and the whole mass of zoospores 

 shows the same movement and behavior as in Py- 

 thium. 



Sexual fusion may occur between two or more 

 thalli in the same cell. One of these, which is desig- 

 nated as the male, puts out a conjugation tube of 

 variable length which fuses with a female thallus 

 (figs. 12. 13, 17). If the two are almost in contact 

 the tube may be reduced to a small swelling on the 

 side of the male thallus at the point of contact with 

 the female. The content of the male then passes very 

 slowly into the female thallus (figs. 12, 13), where 

 the combined protoplasts eventually contract and 

 assume an oval or spherical shape (fig. 16). No de- 

 limitation or differentiation of an egg cell and peri- 

 plasm occurs in the female thallus in preparation for 

 fertilization, according to Vanterpool and Leding- 

 ham, but Truscott's ('33) report that several 

 oospores may be formed in one female thallus sug- 

 gests at least that division of the ooplasm may take 

 place. On the other hand, division may possibly oc- 

 cur after fusion lias been completed. A thick wall is 

 eventually formed around the zygote, and after a 

 short while the empty remains of the male and fe- 

 male thalli disintegrate, leaving the oospores free 

 (fig. 16). Occasionally two or more male thalli may 

 fuse with one female (fig. 17). The conjugants are 

 multinucleate, according to Vanterpool and Leding- 

 ham, but nothing is known about the behavior of the 

 gametic nuclei before and during fusion. 



The formation of oospores may be increased by 

 drying out the soil slightly, and Vanterpool and 

 Ledingham therefore concluded that sex is largely 

 determined by adverse environmental conditions. 

 They described Lagena as dioecious but were uncer- 

 tain whether the zoospores which give rise to male 

 and female thalli respectively come from the same 

 or different zoosporangia. They nonetheless as- 

 sumed that zoospores from sporangia and germi- 

 nated oospores may be of three types: i.e., + an d 

 — > — j a nd _)_, as shown in the diagram below. 



Vanterpool and Ledingham emphasized the strik- 

 ing similarity of Lagena to reduced species of Py- 

 thium and Lagenidium and regarded it as a possible 



connecting link between the Lagenidiaceae and Py- 

 thiaceae. 



L. RADICICOLA Vanterpool and Ledingham, I.e. Pis. 

 1, 2. Figs. 3-7. Truscott, 1933. Mycologia 25: 263. Figs. 

 1-11. 



Thalli 14 X 35 p. or more, exit tubes 4 X 10- 

 20 p.; zoospores 7X 11/*; oospores 10-25^. (For 

 additional details see generic description above.) 



Parasitic in roots of Triticum aestivum, T. durum, 

 Hordeum vulgare, Secale cereale, Agropyron 

 repens, Zea mays, and other wild grasses in Ontario 

 and Saskatchewan, Canada. 



According to Truscott, this species may occur on 

 a number of wild grasses, but Vanterpool and Led- 

 ingham found it to be more limited in host range. 

 Avena sativa, A factua, Agropyron Tenerum, A. 

 spicatum, Bromus biennis, Poa compressa, and 

 Sinapsis arvensis remained immune to attack when 

 grown among infected wheat plants. Lagena radi- 

 cicola causes a root disease which is characterized 

 by stunted, curved roots. The fungus has a predilec- 

 tion for cells in the root tip, and its interference 

 with nuclear and cell division doubtless leads to 

 the shortening and curvature of the roots. In- 

 fected roots have yellowish-brown lesions in the re- 

 gion of infection and the root system as a whole is 

 reduced. No enlargement of cells nor hypertrophy 

 of roots have been observed. The stems of infected 

 plants are considerably shorter than those of normal 

 specimens, while the leaves become pale-green and 

 lighter in color. 



The thalli described by Truscott from Toronto 

 were more elongate, cylindrical, tubular, and 

 branched than those found by Vanterpool and Led- 

 ingham in Saskatchewan, and it is thus evident that 

 the thallus of L. radicicola may vary markedly in 

 size and shape. Truscott reported and figured com- 

 pound oospores (fig. 18) and found evidence that 

 as many as six oospores may possibly be formed in 

 one female thallus. 



DOUBTFUL GENERA 

 RESTICULARIA 



Dangeard, 1891. Le Bot. 2 : 96. 



(plate 24) 



Thallus intra- and extramatrical, broadly elon- 

 gate, tubular, vesicular and filamentous; irregular 

 and undulating in contour, constricted at irregular 

 intervals, witli numerous short protuberances and 



▼ ! 



Zoospores — (±) thallus — zoosporangia — zoospores 



--►Zoospores-^ + > t|™]J"s- 00 e » iu , m \-oospore-zoospores ■ 

 -^■/.uobpurii, ^ — ^ thallus — anthendium/ ' 



