ON ACTINOCOCCUS AND PHTLLOPHORA. 173 



thus developed. In between the cells of the medulla the filaments of the 

 parasite branch and some of them grow ont in the direction of the 

 cortex. These form the shoot-part of the plant, the former acting as 

 root-portions. The filaments do not enter any cells of the host, but 

 simply force their way in between them along the middle lamella. In 

 some way, however, they become connected with the cells of the 

 medulla of the host-plant, secondary pits being formed between the 

 cells of both organisms. 



The normal cells of the medulla of Phyllophora as a rule contain 

 large quantities of starch. This store of food-material is the chief 

 source of food for the parasite. The parasite, therefore, first of all, 

 takes possession of this starch, and in older plants we find that the 

 starch of the host has disappeared from the cells of the medulla, the 

 cells of the parasite now being filled with starch. For this reason it is 

 easy to differentiate the two organisms by adding iodine, when the 

 parasite will turn dark blue, the cell-contents of the host remaining 

 unstained. 



From the filaments which are found in the medulla of the host 

 arise, as already mentioned, the shoot-filaments. They grow in a 

 direction chiefly towards the flat surface of the spermophores, which 

 are infested by the parasite. The filaments soon reach the cells of the 

 cortex, and passing out between the filaments of this layer, they branch 

 outside the host, and gradually the nemathecium of Actinococcus 

 subcutaneus (Lyngb.) K. Rosenv. is formed on the external surface of 

 the host-plant. Numerous filaments arise from the root-portion, and 

 by repeated branching the internal vegetative portion (intramatrical 

 filaments) and the external portion (extramatrical filaments) assume 

 iarge dimensions (Plate XVII., Fig 2). The external filaments foim a 

 mass of radiating rows of cells, often branched at the base, which in 

 the end give rise to the tetraspores (Fig. 6), 



The parasite is unable to pierce the outer covering of the host, when 

 entering the latter. It can only attack the latter through the anther- 

 idial ostioles. On the other hand this outer coat is easily pierced when 

 the same filaments are passing out to form the nemathecia. In this 

 case they have a firm backing in the solid structure of the medulla of 

 the host-plant. The apex of a filament which is passing through the 

 outer wall of the latter seems to affect the surrounding substance in a 

 peculiar way. This is otherwise quite homogeneous in structure, but 



