THE ENDO‐EXOGENOUS METHOD OF GROWTH AND DEVELOPMENT OF CHYTRIDIUM LAGENARIA

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IN THE past decade and a half interest in the lower, relatively simple fungi like the chytrids has been increasing very rapidly, as is attested by the large number of papers which have recently appeared in mycological literature, and during this time almost a score of new genera has been added to this group. Many of these contributions, however, have been primarily systematic and have dealt largely with the occurrence and distribution of old and new species in different parts of the world. While such studies are of fundamental significance in relation to the problems of phylogeny and evolution of the fungi, they have, none the less, very often subordinated intensive study of individual species to general surveys and theoretical speculation. Frequently they have been based on isolated stages of development and thus have left wide gaps in our knowledge of the life cycles of the species presented as well as their degree of pathogenicity, host range, and host-parasite relationship. Furthermore, the accompanying drawings which are intended to illustrate the developmental stages are often highly schematized and diagrammatic, and fail to show adequately the critical, distinguishing structural characteristics. As a consequence many of the genera and species are poorly defined and often based on characters which with more intensive study may prove untenable. Thus in our present state of knowledge the genera Rhizophidittm, Phlyctochytrium, and Phlyctidium, for example, are distinguished only by slight differences in the character of the intramatrical vegetative portion of the thallus, and in the instance of a large number of fragmentarily known species it is impossible to assign them to any of these genera with certainty. Characters such as size and shape of zoosporangia, resting spores, and apophyses; number, length and diameter of exit tubes; size and shape of the apophyses, and extent and distribution of rhizoids, etc., are within certain limits often greatly modified by food supply and other environmental factors. In a culture of Diplophlyctis intestina, for instance, which the author isolated by zoospore infection from a single zoosporangium and has now been growing in cooked Nitella internodes for nearly ten years in the laboratory, the zoosporangia may vary tremendously in size, and in exceptional cases show almost any conceivable variation in shape. Elongated cylindrical, flat, dome-shaped, reticulated, and branched zoosporangia with from 1 to 8 exit tubes have often been found (Karling, 1930), and were it not for the presence of the apophysis and rhizoidal system as well as the more or less constancy in range of size and behavior of the zoospores one might readily mistake the thallus for that of another genus. Furthermore, the apophysis also may vary greatly in size and shape,