. La morphologie comparative et de la biologie des champignons, bactéries et mycetozoa . La morphologie des plantes ; Champignons ; myxomycètes ; bactériologie. Chapitre V.-EXAMEN COMPARATIF.-PERONOSPOREAE. ^37 et en particulier des genres, peuvent être prises principalement par les formations de gonidial, tandis que le peu d'espèces qui n'ont pas gonidia ne sont pas classés facilement. Les principales caractéristiques de la formation d'gonidia des genres et sous-genres de l'Peronosporeae sont comme suit :- Pythimn. Une cellule permanente, habituellement la cellule terminale d'une branche, est délimitée par une paroi transversale et devient une cellule-mère (sporange). La gélatine

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. Comparative morphology and biology of the fungi, mycetozoa and bacteria . Plant morphology; Fungi; Myxomycetes; Bacteriology. CHAPTER V.—COMPARATIVE REVIEW.—PERONOSPOREAE. ^37 and especially of genera, may be taken chiefly from the gonidial formations, while the few species which have no gonidia are not easily classified. The main features in the formation of gonidia in the genera and subgenera of the Peronosporeae are as follows :— Pythimn. A persistent cell, usually the terminal cell of a branch, is delimited by a transverse wall and becomes a spore-mother-cell (sporangium). The gelatinously thickened wall at its apex suddenly expands into a thin-walled spherical vesicle, and into this at the same moment the whole of the protoplasm of the cell, which is hitherto undivided or has only shown transitory beginnings of division, streams rapidly, within a few minutes' time at most; there it breaks up at once into a number of swarm-spores, which issue from the delicate swelling vesicle and finally germinate. The sporangia in some species are of the same form as the gonidia of Phytophthora (Fig. 64), —round or ovoid vesicles prolonged at the extremity into a neck or beak, in the apex of which the swarm-spores are formed ; in others any portion, and often a very long portion, of the cylindric filamentous thallus-tube is delimited to form the sporangium, and its apex in which the swarm-cells are formed is then a small knob-like enlargement at the extremity of a branch, but is not otherwise distinguished by any particular form. There is usually no strict regularity dis- cernible in the arrangement of the sporangia. In species with vesicular sporangia the fila- ment which bears them often grows on into the empty spor- angium from the point of its insertion, or through its entire lengthj and then forms a new terminal sporangium as in Saprolegnia (see p. 46). A certain kind of regular ar- rangement and succession oc- curs in one species only, Pythium intermedium, and i

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