PLASMODIOPHORALES 



The genus Membranosonts has been regarded as a 

 synonym of Sorodiscus, but inasmuch as its inclusion 

 in this genus as well as in Sorosphaera is highly 

 questionable at present it seems advisable for the 

 time being to discuss it separately. 



MEMBRANOSORUS 



Ostcnfeld and Petersen, 1930. Zeitschr. f. Bot. 

 23:17. 



(PL.\TE 9) 



Cystosori one or more in a cell, variable in size 

 and shai)e ; frequently a hollow, single-layered struc- 

 ture wliich covers the inner periphery of the host 

 cell and conforms to the latter's size and shape ; often 

 oval, disc-like and single-layered, rarely double- 

 layered, occasionally composed of an irregular mass 

 of loosely attached spores or a row of spores ar- 

 ranged in a linear series. Resting spores slightly 

 variable in size and shape ; germination unknown. 

 Plasmodia one or more in a cell, variable in size and 

 shape; often in the form of a parietal layer around 

 the host protoplasm; schizogony unknown. Zoospo- 

 rangia and zoospores unknown. 



In light of present-day knowledge Memhrano- 

 sorus is obviously a doubtful genus which should 

 perhaps be discarded entirely, but until more is 

 known about the Plasmodiophoraceae as a wliole its 

 inclusion in any of the other genera is open to serious 

 question. Wernham's observations have shown that 

 the outstanding character described by Ostenfeld 

 and Petersen, namely, hollow single-layered cysto- 

 sori which line the inner periphery of the host cell 

 and conform to the latter's size and shape, is too va- 

 riable (fig. n-18) to be of significant diagnostic 

 value. The incorporation of Memhranosorus in Soro- 

 sphaera or Sorodiscus is equally questionable if the 

 present-day concepts of these genera are to be main- 

 tained, because only occasionally are cystosori in 

 the form of hollow spheres or double-layered discs 

 developed. By the extreme variability of its cystosori 

 this genus resembles perhaps more closely Lif/niera 

 and Poli/mi/xa. Ostenfeld and Petersen regarded it 

 as closelv related to Sorosphaera and Tetrami/.ia, 

 while Wernham implied tliat it should be incorpo- 

 rated with Sorodiscus. Palm and Burk regarded 

 it as a synonym of Sorosphaera. Cook api)arently 

 overlooked its existence entirely in his monograph of 

 the Plasmodiophorales. 



M. HETERANTHERAE Ostenfeld and Petersen, I.e., 

 fi)i. 1-6. 

 Sornili.iciig Hi'teranlherae, Wernham, 1935. Mycologia 

 3T:-212. PI. IT, 18, ftp. 1,2. 



Resting spores always aggregated in multiitles of 

 four. Globose, ovoid, angular. S.5-5 /x in diameter, 

 hyaline and buff-brown, with smooth. 0.6-1.0 // thick 

 walls : apical ring, collar or operculum lacking. Plas- 

 modia oval, ellipsoidal. 8 ft in diameter, or disc-like, 



flat and often ribbon-shaped. 28-70 /n in length, and 

 encircling the host protoplasm. 



Parasitic on Heieranthera dubia in Ontario and 

 Quebec, Canada; Vermont and New York. U. S. A.. 

 causing marked hyjjertrophy of adventitious and 

 true roots. 



Whether or not the species described by Osten- 

 feld and Petersen, and Wernham. respectively, are 

 identical is not absolutely certain, but since they 

 have the same habitat and distribution, cause the 

 same symptoms, infect the same tissues of identical 

 hosts, and agree closely as to spore size and shape, 

 they are listed herewitli as synonymous. The chief 

 differences so far relate to spore color and variations 

 in the size and shape of the cystosori. Since Osten- 

 feld's and Petersen's material was very scanty they 

 may have missed most of the variations later ob- 

 served by Wernham. Likewise, although Wernham 

 never found a single-layered cystosorus completely 

 lining a host cell, his figure 2 shows that the type of 

 sorus described by Ostenfeld and Petersen was often 

 api)roximated in his material. Tliere is accordingly 

 good evidence that they may have had the same spe- 

 cies at hand. 



Nothing is known about tlie method by which this 

 parasite gets into the roots, but entrance appears to 



PL.\TE 9 

 Membridio.iorus Heterantheroe 



(Fig. 1-3, 6, 19 and 20 after Ostenfeld and Petersen; re- 

 mainder after Wernham; fig. 5 and IS drawn from 

 photographs.) 



Fig. 1. Portion of infected stem of //. fliibia with 10 

 swollen and 5 normal roots. 



Fie. 2. Early infection stage with small granular para- 

 site attached to host nucleus. 



Fig. 3. Young bi- and trinucleate parasites in daughter 

 host cells. 



Fig. 4. Young parasite with three nuclei. 



Fig. .5. Large parietal plasmodium which almost com- 

 pletely envelopes host protoplasm. 



Fig. (i. Large multinucleate plasmodium enveloping the 

 host nucleus. 



Fig. 7. Plasmodium with nuclei dividing promitotically. 



Fig. 8. Plasmodium in which nuclei are about to undergo 

 reduction division. 



Fig. 9. Plasmodium with nuclei which have just under- 

 gone reduction division. 



Fig. 10. Second meiotic divisions. Plasmodium cleaving 

 into resting spores. 



Fig. 11. Cystosorus of young thin-walled resting spores. 



Fig. 12. Flat, almost circular cystorus composed of a sin- 

 gle layer of resting spores. 



Fig. 13. Similar cystosorus with one resting spore pro- 

 jecting beneath. 



Fig. U. Flat, two-layered cystosorus. 



Fig. 15. Cystosorus with resting spores In a row. 



Fig. 16 and 17. Irregular cystosori with loosely attached 

 resting spores. 



Fig. 18. Single-layered cystosorus incompletely lining 

 Inner periphery of host cell. 



Fig. 19. Similar cystosorus completely lining inner pe- 

 riphery of the host cell. 



Fig. 20. Surface view of similar cystosorus. 



