50 PHTCOMTCETEAE 



spores are formed in several species and are smaller than the host cells, 

 lying free from the host wall. They may be smooth or spiny. Sexual repro- 

 duction is unknown. Sphaerita is an incompletely known genus of which 

 S. dangeardii Chatton and Brodsky is parasitic in species of Euglena. 

 The description of the single flagellum attached anteriorly but trailing 

 posteriorly casts doubt on the correctness of its position here since in the 

 genus Pseudosphaerita of the Olpidiopsidaceae the two flagella, attached 

 near the anterior end are unequal in length, the shorter one anterior and 

 the longer one trailing posteriorly. Several other genera are recognized 

 but will not be discussed here. 



Family Achlyogetonaceae. This family containmg three genera, 

 occurs in fresh-water algae, and reportedly in some Nematodes. In the 

 genus Septolpidium, occurring in Diatoms, the fungus elongates within 

 the host cell and by successive septation forms a series of zoosporangia 

 from which the posteriorly uniflagellate zoospores escape through single 

 exit tubes. 



Family Synchytriaceae. In this family we find fungi whose para- 

 sitism is confined largely to the higher plants. Synchijlrium is the chief 

 genus. Its swarm spores possess one posterior flagellum. After settling 

 upon the host, which only occurs in a drop or film of water, the swarm 

 spore dissolves an opening into an epidermal cell and enters as a whole, 

 not leaving an empty cyst attached externally. The presence of the 

 parasite usually stimulates the host cell to hypertrophic growth. This 

 cell may elongate and enlarge to a balloon-shaped external structure as in 

 Erodium cicutarium (L.) L'Her. infected by S. papillatum Farlow, the 

 other cells of the host remaining normal. The enlargement of the epi- 

 dermal cell may be chiefly lateral and inward in some plants so that it 

 does not project from the surface but more or less crushes the adjacent 

 host cells. The enlargement may be both outward and inward, some of 

 the adjacent cells developing hyperplastically and even undergoing hyper- 

 trophy, the result being a wart-hke structure, as in S. vaccinii Thom. on 

 the cranberry, Oxycoccus macrocarpus (Ait.) Pursh. When great hyper- 

 plasia and hypertrophy both occur in the host tissues, the fungi may 

 remain in the inwardly enlarged epidermal cells or by the division of the 

 latter may come to lie more deeply in the massive hyperplastic tissues. 

 This is the case in S. endohioticum (Schilb.) Perc, the cause of the wart 

 disease of the potato, Solanum tuberosum L. M. T. Cook (1945) has made 

 a study of the different types of response by the host to infection by 

 different species of Synchytrium. (Fig. 11.) 



Within the host cell the ])arasite enlarges and soon develops a cell 

 wall. This is reported by von Wcttstein (1921) and von Gutenburg (1909) 

 to contain cliitin, a component of the cell walls of most of the higher 

 fungi. At first the parasites remain uninucleate. By division of the nucleus 



