LAG EN I DI ALES 911 



the formation at irregular intervals of narrow cross walls. In some 

 instances as many as seven segments are produced from a single 

 thallus. These are transformed into reproductive organs. 



In Myzocytium (Zopf, 1884) the young one-celled thallus early 

 becomes torulose, as if it were being proliferated by a yeastlike budding. 

 Here, however, in contrast to the development in Lagenidium, no 

 branches are formed. At from twelve to twenty-four hours after 

 infection the vegetative stage is superseded by the reproductive phase. 

 There are now laid down at the constrictions between the successive 

 swellings very thick two-layered refractive cross walls which divide the 

 thallus into a chainlike series of links. All of the segments thus formed 

 become reproductive organs (Fig. 79 A-B, p. 977). 



In Lagenidium, Myzocytium, Pontisma, and Sirolpiciium single-celled 

 thalli which resemble those of Olpidiopsis are occasionally observed. 



REPRODUCTION 



Nonsexual Reproduction 



The zoospores of the Olpidiopsidaceae and the Sirolpidiaceae are 

 fully formed in the zoosporangium. 



In Olpidiopsis (Barrett, 1912b) the maturing sporangium is at first 

 strongly vacuolate. Changes in the contour of the spherical vacuoles 

 occur at the same time that the discharge tube forms. Further stages 

 involve the sudden disappearance of the large vacuoles, with the 

 protoplasm assuming a finely granular, lighter, more homogeneous 

 aspect, and the appearance in some instances of small vacuoles. These 

 vacuoles ultimately vanish, the protoplasm becomes more coarsely 

 granular, and the spore origins appear. The zoospores become more 

 definitely outlined and initiate movement. The discharge tube then 

 opens and the zoospores escape. The exit tube, Barrett believes, secretes 

 an enzyme which aids in penetration, although evidences for mechanical 

 action were also observed. A similar sequence has been described by 

 Butler (1907) in O. aphanomycis, except that in his fungus a heaping 

 of the protoplasm followed the change in contour of the large vacuoles 

 of the resting sporangium. At this stage Butler supposed that the con- 

 tents became cleaved into relatively large multinucleate masses. Bar- 



