54 The Ohio Naturalist. [Vol. X, No. 3, 



EXPLANATION OF PLATES III AND IV. 



All figures ai-e camera drawings from sections. All except 

 Figs. 1, 3-7, were made with a Spencer 1.5 mm. immersion 

 objective and compensating ocular 4 giving a magnification of 

 approximately 670 diameters. Fig. 1 was drawn with an 8 mm. 

 objective and 4 ocular giving an approximate magnification of 

 125 diameters; Fig. 3 with the 1.5 mm. objective and 3 ocular, 

 magnification 533; Figs. 4-7 with objective 1.5 and ocular 12. 

 magnification 2130. The plates were reduced to 2-3 of their 

 original size exactlv eliminating the enlargement due to the 

 camera and rendering them the same size as seen in the 

 microscope. 



PL.\TE III. 



Fig. 1. A tangential section through the hypoderniis of the wing of the 

 petiole of the Ragweed, showing the general relations of the 

 parasites to the tissue of the host. R. Sp. Resting Spores, 

 Z. Sp. Zoosporangia. 

 Fig. 2. A cell with numerous amoebid zoospores imbedded in the host 

 cytoplasm; one pair of zoospores conjugating; cell distorted 

 by an adjacent zoosporangium measuring 45 x 60 n, note 

 slight degree of injury. 

 I'ig. 3. A tangential section of a host cell wall showing perforations 

 where the parasites entered. 

 One of the zoospores from Fig. 2. 

 Zoospores just beginning to conjugate. 

 Conjugating zoospores. 

 Conjugation complete. 



A cell with two young zygotes, each binucleate, and several 

 unconjugated zoospores; note cellulose plugs marking the 

 points where the parasites entered. 

 A young zygote. 

 Zygote nearl_y full grown. 

 A young resting spore; note slight injury to the nucleus and 



cytoplasm of the host cell. 

 Two ripe resting spores within same host cell; each binucleate 

 though the nuclei of the lower spore do not lie within the 

 plane of section. 

 Fig. 1.3. A cell with two young parasites; a probably the first division 

 (amitotic) of the zoospore; b, a plasmodiuin with four nuclei; 

 on the wall are shown the plugs marking the points of 

 entrance. 

 Fig. 14. A young Plasmodium with eight nuclei most of which are in 

 process of ainitosis ; central vacuole developed unusually early. 

 I'^ig. 1"). A Plasmodium with about GO nuclei; central vacuole beginning 



to appear; note relations of parasite and host nucleus. 

 Fig. If). A larger plasmodium with well developed central vacuole lying 

 in the chlorenchyma of its host; note slight injury beyond 

 mechanical distortion. 

 Fig. 17. A full sized plasmodium with very many nuclei. 

 I'ig. IS. A ripe zoosporangium; opening at top may he natural or due 

 to knife. 



