128 PROTISTS AND DISEASE 



leaves. Seedlings were infected by sprinkling them with 

 water in which tumours which had been dried and pounded 

 in a mortar were suspended. The vegetative period begins 

 as an amoeba having one or two nuclei lodged in the cyto- 

 plasm of a procambial cell of the host-plant. The amoebi- 

 form parasite grows, its nuclei increasing in number, and 

 it is termed a plasmodium. Several such may be 

 contained in the same host-cell which is then greatly hyper- 

 trophied. Mitoses are frequent in the nuclei of the host- 

 cells. 



The authors kindly gave me a section of one of the 

 Veronica tumours. Fixed in Bouin's solution (formol 10 c.c., 

 saturated aqueous picric acid 30 c.c., and crystallisable 

 acetic acid 2 c.c.), and stained in Benda's iron haematoxylin, 

 it shows the features described by the authors very clearly. 



The dividing trophonuclei at metaphase are cruciform, 

 the elongated nucleolus having a ring of chromatin around 

 it. The nuclei shown in Fig. 35, 5, are in a prophase : 

 Maire and Tison give a similar drawing and state that it 

 shows " separation of idiochromatin from trophochromatin 

 in prophase of nuclear division." 



The spherical sori with spores arranged peripherally 

 round a central space are a striking feature in the sections. 

 A chromidial stage followed by two ordinary reproduction- 

 mitoses ends in spore-formation, which differs from that of 

 Plasmodiophora only in the formation of a sorus. 



Spongospora scabies is the cause of corky scab of the 



