ON ACTINOCOCCUS AND PHYLLOPHORA. 175 



already mentioned, the effect of adding iodine is to show up the cells 

 of the parasite more clearly, as the latter has absorbed all the starch 

 out of the cells with which it has come in contact. It is easy to make 

 out the shape of the starch-grains of Phyllophora (2, p. 22, Fig. 26 n, 

 8 — 10), but impossible to detect any definite structure and shape in the 

 case of the very minute elements composing the starchy mass found in 

 the cells of Actinococcus subcumneus. Those parts of the primitive 

 th alius of the latter, which are presumably most actively growing, as, 

 for example, the apices of the filaments of the shoot-portions, contain 

 no starch or only very little indeed. The root-filaments are usually 

 completely filled with starch. 



The internal cells of the whole parasitic cushion vary much in size 

 (2, Fig. 30). The smallest are barely 6 p in diameter, the largest 

 measure 60 by 30 p.. The latter do not always belong to the parasite, 

 but often form part of the tissue of the host. They are more or less 

 round, the cells of the parasite being slightly elongated as a rule. The 

 latter are connected with one another by fine cytoplasmic strands. The 

 cells of Phyllophora also possess numerous pits, by means of which 

 their cytoplasm is continuous. Only on rare occasions is it possible to 

 make out any connexion between the cells of the parasite and the host. 

 In cases where the parasite has been growing in the host for some 

 time, the filaments of the former often may grow a considerable dis- 

 tance down into the tissue of the thallus of Phyllophora in order to 

 absorb more food-material for the cells of the tetrasporic fructification. 



The extramatrical filaments gradually form the nemathecium of the 

 parasite. The outermost radially disposed filaments gradually develop 

 into tetrasporangia. Each cell of these usually unbranched fertile 

 threads, gives rise to four tetraspores, with the exception of the two to 

 four apical cells (Fig. 7). The inner and lower cells of the fertile fila- 

 ments also remain sterile. The whole fertile nemathecial layer is in 

 itself about 150 — 200 p deep. The sterile apical cells contain some 

 clear, frothy cytoplasm and a distinct, though as a rule very much 

 reduced, rhodoplastid. They are usually larger and longer than the 

 tetrasporangia. 



The tetraspores are formed by cruciate division, the first cross-wall 

 formed being placed at right angles to the long axis of the fertile fila- 

 ment. The spore mother-cells measure 12 x 16 p, the four nuclei 

 being formed before the formation of cell-walls gives rise to the four 

 tetraspores. 



