KHIZOPUS NIGRICANS. 15 



11 )p(>{U's oraiiij;o. the cln'oiiititin blue, the luiclcolus and ])f()t(Md crvstal- 

 loitls red, ami the cell wall either blue or oranoe. 



For tixing" liuids the mixtures of Flennning, llerinanu, and ]\IerkeI 

 were used with verv g-ood results. Eisen's fluid u-avo some very tine 

 results, ])ut was little used. An exposure of one hour to Flemmino-'.s 

 fluid, followed by twelve to twenty-four hours in ^lerkeFs fluid or 

 chrom-acetic aeid, o-ave especially iine preparations, not being so nuuh 

 l)laekened as when exposed longer to the osmic acid. 



I am deeply indebted to Dr. Robert A. Harper of the I'niversity of 

 AVisconsin. and to Dr. Erwin F. Smith, Dr. Rodney II. True, and ]Mr. 

 Karl F. Ki'llerman of the United States Department of Agriculture 

 for many valuable suggestions and criticisms given during the prog- 

 res ; of the work. 



t 



RHIZOPTJS NIGRICANS I.hrbg. 



The general morphology of Ii/ilsojms has been Acry well described 

 by the earlier authors. 



The spore in germinating sends out a tube which branches until a 

 tangled mycelium is formed in the substratum. This mycelium sends 

 up from various points ar>rial hypha?, which are erect at flrst and form 

 a delicate white grpwth in the cultures. After these h^'ph* reach the 

 lieight of one or two centimeters thev bend over and o-row horizon- 

 t:illy along the surface of the substratum. 



When one of these stolons has grown in this direction for a short 

 distance, it forms a swelling at the apex two to four times the diame- 

 ter of the stolon, and out of this grow from two to six branches, one 

 of which is in reality a continuation of the stolon, while the others 

 grow into sporangiophores. (PI. I, flg. 1.) If this swollen portion of 

 the stolon comes in contact with the substratum or the sides of the cul- 

 ture dish, a few rhizoids are sent out which tirral}' anchor it, and, in 

 case the}' penetrate any nutritive substance, these doubtless aid in 

 nourishing the sporangiophores. The stolon continues gTowing- out 

 and forming these grouj^s of sporangiophores at intervals, and linally 

 ends with such a group at the apex. Each sporangiophore bears a 

 single spherical sporangium. 



In healthy stolons, especially if they are growing rapidly, the pro- 

 toplasm is almost continuall}' streaming in one direction or the other. 

 This has been fully described by Arthur (ISUT), who considers that it 

 is principally due to evaporation of moisture from the surface of 

 exposed parts, together with the constant taking in of water b_v the 

 hyphte that are in the substratum. In his conclusion he expresses 

 the opinion that ''the movement is an incidental feature in the life of 

 the plant." Further mention of this paper will be made in connection 

 with the distribution of the protoplasm in the sporangium. 



