62 



PLASMOmOPHORALES 



be sufficient reason for separating the two species. 

 Light appears to be the dominant factor in infection. 

 No infection occurs in roots exposed to light even 

 when other environmental conditions are optimum, 

 according to Cook ('27). 



In this connection it may be noted that Hildebrand 

 ('34', PI. I, fig. 5) observed cystosori of indefinite 

 size and shape in diseased rootlets of strawberries 

 in Canada. Whether or not these resting spores re- 

 late to Lif/niera or another genus is uncertain at 

 present, since Hildebrand made no further study of 

 the organism in question. 



L. PILORUM Fion and Gaillat, 193.5. Bull. Soc. Mycol. 

 France H : ,390. PI. 10. 



Resting spores aggregated into globose and ir- 

 regular clusters or cystosori, or lying end to end in 

 a linear series ; oval, spherical, 4—6 /t, or angular 

 and polyhedral when compressed together, with thin 

 Iiyaline smooth walls. Plasmodium filling the en- 

 larged base or tip of the host cell ; schizogony ques- 

 tionable ; Plasmodium apparently segmenting into 

 either zoosporangia or resting spores. Zoosporangia 

 (?) oval, spherical, angular and compressed, 4— 6 /x 

 (.'') with tliin, smootli hyaline walls, opening by the 

 rujjture of a thin localized area. Zoospores small, 

 pyriform, up to 1 /x (?) in diameter; flagellum of 

 same length as spore body. 



Parasitic in the root hairs of Poa annua in France, 

 causing marked local hypertrophy ( ?). 



Fron and Gaillat's drawings and descriptions of 

 the developmental stages of this species are very 

 brief and inadequate, and it is not clear whether the 

 zoos]Jores arise from germinating resting spores or 

 zoosporangia like those described by Cook ('26) for 

 L. Jnnci. The latter view seems more plausible be- 

 cause figures 7 and 8 by Fron and Gaillat show what 

 appears to be several zoospore initials within a single 

 unit of the aggregate; whereas the resting spores of 

 most plasmodiophoraceous species are now rather 

 generally believed to form but one zoospore apiece. 

 If Fron and Gaillat's measurements are correct, this 

 species is characterized by unusually small zoo- 

 spores. Cook ('26, '33) regarded L. piloriim as syn- 

 onymous with L. Jiinci, because it also occurs in Poa 

 annua and agrees with the latter in life cycle and 

 resting spore size. The chief differences are zoospore 

 size and the fact that L. pilorum causes hy])ertrophy 

 of the host cell, according to Fron and Gaillat. Cook 

 maintained that such hypertrophy is not due to the 

 stimulus of the parasite but that L. pilorum may 

 fortuitously infect root hairs which are already 

 swollen. In further support of his belief that the two 

 species are identical, he Jjointed out that L. Junci 

 occasionally attacks swollen hairs also. Schwartz 

 ('11) likewise observed that normally swollen root 

 hairs (fig. 27) may sometimes become infected witli 

 L. Junci. It seems almost too accidental, however, 

 that all the infected root hairs shown in IVon and 

 Gaillat's (fig. 1) are greatly enlarged at the ti)). 

 Nevertheless, it is not entirely improbable that L. 



Junci and L. pilorum are identical, but until more is 

 known about the latter siiecies and host range, its 

 identity and validity will remain questionable. 



L. VERRUCOSA Maire and Tison, I.e. 1911, Ann. 

 Mycol. 9: -'35. PI. 11, fig. 39-41; pi. 12, fig. 43-46. 



Resting spores occasionally aggregated in a linear 

 series, more often in globular, ellipsoidal solid, 

 rarely flattened, and disc-shaped, or hollow balls ; 

 resting spores oval, spherical, 4— .5 /x in diameter, 

 angular and polyhedral when compressed, with 

 fairly thin, hyaline verrucose walls. A})parently giv- 

 ing to rise to zoospores in germination, which infect 

 the host. Plasmodium partly or completely filling the 

 host cell ; giving rise to one or more cystosori ; schi- 

 zogony reduced or lacking entirely. Zoosporangia 

 and zoospores unknown. 



Parasitic in the root hairs and roots of Veronica 

 arvensis (Maire and Tison, I.e.), Beta vulgaris, 

 Chenopodium album, Bromus sp., and Fcstuca sp. in 

 France (Guyot, '27), without causing hypertrophy 

 of the host tissue. 



This species is imperfectly known at present, and 

 many of its critical stages remain to be studied. As is 

 sometimes true of the previous species, the shape and 

 structure of the cystosori de])end to a large degree 

 on the character of the host cell. ^^Mlen the cystosori 

 occur in elongate narrow root hairs, they may consist 

 of a linear series of resting spores, but if they de- 

 velop in the cortical parenchyma cells, they usually 

 have the form of more or less solid, globose and ellip- 

 soidal balls. 



Guyot regarded this species as a variety of L. 

 Junci, because the characters of his specimens of L. 

 verrucosa seemed to merge imperceptibly with those 

 of L. Junci. Cook ('33), after examining material 

 submitted by Guyot. and Claire and Tison found no 

 difficulty in distinguishing L. Junci and L. verrucosa. 

 However, the warts on Guyot's specimens were 

 found to be much less pronounced than those on 

 Maire and Tison's material. Palm and Burk did not 

 regard the presence of warts as a specific character, 

 since in a single species of Sorosphaera on T'eronica 

 americana they found both smooth and warty spores 

 with all degrees of gradation between the two types. 

 Hence, they regarded L. verrucosa as identical to L. 

 radicalis or L. Junci. The development of smooth and 

 warty spores in a single species is not at all uncom- 

 mon among fungi, and Palm and Burk were probably 

 right in their conclusions. !More intensive study of the 

 develojjment, variations, and host range of L. verru- 

 cosa is. however, essential. 



L. ISOETES Palm, 1918. Svenska Bot. Tidsskr. 12:328. 

 Fig. 1-3. 



Resting spores sometimes in more or less loosely 

 aggregated clusters, more often in hollow balls which 

 fill the host cell and conform with the latter's shape. 

 Resting spores oval, almost spherical, angular and 

 l)olyhedral when compressed, .5X6—8 fx, with thin, 

 smooth brownish-colored walls. Plasmodia jjartly or 



