2 ARKIV FÖR BOTANIK. BAND 12. N:0 9. 



on his part toward me. I am also indebted to my friend, 

 the cytologist Professor 0, Rosenberg for much good advice 

 and for personal kindness during my sojourn at the Univer- 

 sity of Stockholm. A journey in foreign countries robbed 

 me of the best part of the year 1911, so that only now I 

 have had leisure to collect my results into this paper. 



If not an excellent treatise by René Maire and Adrian 

 Tison: La Cytologie des Plasmodiophoracées et la classe des 

 Phytomyxinae (Annales Myc. 1909) and several other papers 

 on the Plasmodiophoraceae by the same authors, b}^ Blom- 

 FiELD and Schwartz a. o. had been pubhshed in the mean- 

 time, the records of Lagerheem would have been of greater 

 moment. In order to avoid repetitions we shall now only 

 report his investigations on the teratology of the species of 

 Veronica, when they are infected by Sorosphaera Veronicae, 

 and we are also going to publish a new genas of the family 

 of the Plasmodiophoraceae together with some critical remarks 

 on other forms. 



Plasmodiophora Brassicae Wor. 



After the monography by Woroni:^^ on this fungus se- 

 veral other authors have undertaken investigations of it 

 (among which Eycleshymer,^ Wakker,- Nawaschin,^ Pro- 

 wazek,^ Maire and Tison ^). 



Nawaschin gave the impulse to the study of the cyto- 

 logy of Plasmodiophora, and his results, which are put down 

 in his above-named excellent paper, give almost exactly the 

 true figure of the cytology of all fungi, belonging to the 

 Plasmodiophoraceae. Nawaschin points out that plurinuc- 

 leated amoebae with peculiar nuclear divisions are found in 

 the host-plant; these divide into smaller ones, and by divisions 

 of the host-plant the amoebae are spread in the tissues. 

 After further divisions of the nuclei and the amoebae 

 (the two kinds of division, however, take place independ- 

 ently of each other) these latter ones change their nature 

 shortly before the spore-formation in that their nucleoli, 

 which were hitherto very conspicuous, entirely disappear. 

 Still new nucleoli will be formed and a common mitosis is 

 going on; finally the amoebae are divided into as many parts. 



