864 REPORT— 1897. 



due to either bilateral or radial biological symmetry, or to bilateral or radial 

 topographical symmetry. Zonal and azonal formations are contrasted, and the 

 latter shown to be rare and atypical. 



6. The Transition Region of the Caryophyllales. 

 By Frederic E. Clements. 



The history of the investigation of the transition region is discussed at con- 

 siderable length. After a concise sketch of the histogenetic changes in the transi- 

 tion reoion in general, the details of the process are given for selected genera, 

 Dianthus, Portulaca, Allionia, Phytolacca, Polygonum, and Rumex. Three types 

 of transition may be distinguished with respect to the constitution of the bundle 

 trace of the cotyledons: holostelar, where the trace is composed of the entire 

 vascular system of the hypocotyledonary stele ; prototracheidal, when the proto- 

 tracheids are the xylem elements to pass into the cotyledons ; metatracheidal, when 

 the cotyledonary trace is formed by the metatracheids. With reference to the per- 

 fection of the transition in the hypocotyl, the transition may be truncate or com- 

 plete. In the first case, the xylem and phloem reach the cotyledons in centripetal 

 or secantial orientation ; in the second, the orientation is centrifugal, and the stele 

 becomes collateral. 



7. Note on Pleurococcus. By Dorothea F. M. Pertz, Cambridge. 



Cultures of Pleurococcus in nutritive solutions were made during the winter 

 months, from November to April. They did well in Knop'a solution, -2 per cent., 

 in sterilised glass dishes and flasks, which were placed in different situations ; in the 

 laboratory, in a greenhouse, and out of doors. 



Separate clusters of Pleurococcus in hanging drops of the same solution were 

 also observed as continuously as possible. These drops were suspended in carefully 

 sterilised moist chambers, which were kept for several weeks, in one case for two 

 months. 



The chief difficulties met with were, first, to obtain the Pleurococcus in ab- 

 solutely pure condition, and then to keep it sufficiently aerated without running 

 any risk of making the culture impure. Both the ' globular sporangia ' and those 

 of ' elongated or quadrangular form,' observed by Chodat, occurred frequently, and 

 they seem undoubtedly to be produced by the transformation of normal Pleuro- 

 coccus-cells. Individual sporangia were repeatedly selected for special observation, 

 and the process by which they break up into separate spores was noted at all its 



stages, 



The filamentous form described by Chodat never occurred. 



MONDAY, AUGUST 23. 

 The following Papers were read : — 



1. Antherozoids of Zamia integrifolia.^ By Herbert J. Webber, M.A., 



Washington, D.C. 



The occurrence of motile anthero/oids in Zamia confirms their recent discovery 

 in Gingko and Cycas by the Japanese investigators Hirase and Ikeno. The develop- 



' For fuller details see ' Peculiar Structures Occurring in the Pollen Tube of 

 Zamia,' Bot. Gazette, vol. xxiii., June 1897, p. 153 ; ' The Development of the Anther- 

 ozoids of Zamia,' Bot. Gazette, vol. xxiv., July 1897, p. IG ; ' Notes on the Fecunda- 

 tion of Zamia and the Pollen Tube Apparatus of Gingko,' Bot. Gazette, vol. xxiv., 

 October 1897, p. 255. 



