SOUOSPIIAKRA 



13 



both cell limit ipliiaf ion and itll cnlarmciiicnt witli 

 tin- lattiT proi-css playiiiii tlif (loniinaiit role in tin- 

 lati-r stages of divclol)nunt. Since the (larasite has 

 a ])redilcetion for the provascular strands in tlic 

 aj)ieal nieristem. the tumors may involve the entire 

 stem in instances of severe infection. In such eases 

 the priuiordia of the stems and leaves are reduced 

 to a mass of cells in which |)ith. cortex, etc., are indis- 

 tingiiish.-ihle. In less extensive infections only small 

 portions of the stem hceome involved, and the normal 

 growth of the plant is not seriously artectcd. .\ccord- 

 ing to Lagerheim. the development of the vascular 

 ring is suppressed in the region of infection, while 

 in the outer cortex the collenchyma is still present. 

 The rem.iining cortical cells become tangentially 

 oriented in growth and greatly enlarged. The ejiider- 

 mal cells become isodiametric. and the gu.ird cells of 

 the stomata are often considerably enlarged, with 

 the pore itself abnormally wide. 



.\lthough infection has not been observed. S. J'e- 

 ron'icae appears to make its initial entrance in the 

 apical meristem. because the youngest plasmodia and 

 smallest galls occur in or near the apex. Blomtield 

 and .Schwartz succeeded in jiroducing tumors on Ve- 

 ronica seedlings by si)raying them with water con- 

 taining crushed cystosori and found single, isolated 

 infected cells close to the growing point. The amoe- 

 bae of the parasite are apparently unable to pass 

 through the walls into adjacent cells. According to 

 Blomtield and .Schwartz, and Cook ("33). they are 

 passively distributed by the repeated division of in- 

 fected provascular cells. If the young plasmodia un- 

 dergo schizogony, as Maire and Tison reported, the 

 number of amoebae is greatly increased, and by re- 

 peated division of infected cells, large diseased areas 

 are soon formed. In the early stages of the disease the 

 presence of the [larasite apparently does not inhibit 

 cytokinesis of the host cells, but later on after they 

 have become enlarged the latter lose the ability to di- 

 vide. The enormously enlarged nuclei, however, un- 

 dergo several mitoses with the result that the infected 

 cells become multinucleate (fig. 3). Division of the 

 host nuclei is greatest at the close of the vegetative 

 stage of the parasite, but with the onset of the sporo- 

 gonie ])hase mitosis ceases. At this stage the host nu- 

 clei become distorted (fig. .5), more densely stainable, 

 (fig. i). and eventually disintegrate (fig. Vt). By the 

 time the cystosori are mature, only atroi)hied and de- 

 generated nuclei are to be found, according to Bloni- 

 field and Schwartz. On the otlier hand. .Maire and 

 Tison rei)orted that the nuclei as well as ))]astids and 

 starch grains may jM-rsist long after the sori have ma- 

 tured. 



In the early stages of infection only slight en- 

 largement of the host cells occurs, but as the plas- 

 modia increase in size, marked expansion takes place. 

 In exceptional eases infected cells may enlarge to 20 

 times their normal diameter. Sorosphaera J'eronicae 

 accordingly not only causes enormous cell enlarge- 

 ment but also prevents cell diflferentiation. .\djacent 

 healthy cells as well as stomatal guard cells may also 

 be stinuilated to enlarge by the presence of the para- 



site. .\s is shown in figure 2. there ,ai)))ears to be no 

 visible .■intagonisni between tlie proto])l;ism of the 

 host and pathogen. The I.itter lies embedded in the 

 host eytoiilasm and in the young stages may be 

 closely associated with the host nucleus. Infected 

 cells may contain numerous jilastids and starch 

 grains, but these are not so abundant as in the adja- 

 cent healthy cells. According to I.agerheim. ei)idcr- 

 mal cells in the infected regions .ire richer in crystals 

 th.in tiiose in healthy j)ortions of the stem. 



Slugs frequently feed on the galls, and it is be- 

 lie\ed th.it they play a signifie.int role in spreading 

 the disease. Most tumors soon soften and decay, lib- 

 erating the cystosori into the soil, where the resting 

 sjiores germinate. When new plants push up through 

 the soil, their ajjices a])l)arently become infected. 

 Sorosphaera J'eronicae has never been found jiara- 

 sitizing the roots. 



Nematodes also may cause galls on Veronica which 

 arc strikingly like those ))roduced by .V. J'eronicae 

 and may easily be mistaken for them. I''or this rea- 

 son Cook ('33) regarded with susijieion the rejjorts 

 of I.agerheim and Winge of the presence of the para- 

 site in a large number of J'eronicae species in Nor- 

 way and Sweden. 



S. RADICALIS Cook. 1933. .\reh. Protistk. 80: .'01. PI. T, 

 fig. 10, 11. 

 S. nuliriile Cook and Sclnvart/.. lfl-'9. .\iiii. Hot. 43: 86. 

 PI. 2. 



Cystosori single and Jiartly filling host cell, hol- 

 low, rarely spherical, 20 yu,, usually oval, ellipsoidal 

 .and elongate, 1(5-20 fj. X 20-.57 /u,, bright yellowish- 

 brown ; including up to 500 spores. Resting spores 

 oval, 3 X ^ /i. with thin yellowish-brown, smooth 

 walls ; producing one zoos])ore in germination. Zoo- 

 spores oval and sl)lierical, 2-3 /x. with an anterior 

 flagellum (.'') l—ti/x long. Evanescent zoosjjorangia 

 unknown. Plasmodia single and partly filling host 

 cell. 20-60 /J. ill diameter, producing one cystosorus ; 

 schizogony lacking (.'). 



Parasitic in the root hairs only of Poa fluiians 

 MoniVia caerulea, Catabrosa aquaiica, and other 

 grasses in England, causing localized enlargement 

 of the infected cells. 



This species is distinguishable from .S'. J'eronicae 

 jirimarilv by its oval, ellipsoidal and elongate cysto- 

 sori which are also much larger ;iiid com])Osed of a 

 greater number of small resting sjiores. In .addition, 

 its nuclei are considerably smaller. While .V. radicalis 

 may occur in the same vicinity with and infect some 

 of the hosts of Lifjniera J unci as well as L. verrucosa 

 and L. piloriim. Cook and Schwartz maintained that 

 it is ()uite distinct. However, it is to be noted here 

 that these Lifjniera s|)ecies may also occur in locallv 



' In recent correspondence with the aiitliiir. Prof. .J. T. 

 Barrett, College of .Agriciiltnre, Califdrnifi rniversity, re- 

 ported that he had fonnil what lie helieves to he S. ridlirnlis 

 in roots of I'oa annua on the eoUejie rani]>iis. In addition to 

 cystosori and resting spores, he ohserved thin-walled spo- 

 ranjria which produce hifhifrellate, hettrocont zcM)spores. 

 Harrett thus confirms I.edingham's previous n-)iort of sudi 

 /,oo,..pores in Sftro.splifiern. 



