1914] FROMME—AECIDIUM CUP 7 



together in groups, often with an annular arrangement, and the 

 older ones are found in the center of the group and the younger at 

 the margins. This distinction is of some importance in collecting 

 material for study, as it is usually necessary to make several col- 

 lections of the forms from a diffused mycelium in order that all 

 stages may be represented, while all stages may be present in a 

 single fixation when the aecidia are from a localized mycelium. 



All of the material was fixed in the field. Small segments of 

 leaves or stems bearing aecidia were immersed immediately after 

 removal in a small vial of fixing solution. Of a number of fixing 

 solutions tested, weak and medium Flemming's were found to give 

 the best results. The segments were allowed to remain in the fixa- 

 tive for 48 hours, after which they were washed, hardened, and 

 imbedded in paraffin. The sections were stained for the most part 

 with the safranin, gentian violet, and orange G combination, 

 although iron-hematoxylin was used to some extent for comparative 



study. 



The development of the cuplike aecidium 



Puccinia Claytoniata proved to be an exceptionally favorable 

 form for study. The cells and nuclei of the fungus are large, and 

 the host tissue is soft and succulent and apparently permits rapid 

 penetration of the fixing solution. The vegetative mycelium that 

 precedes the formation of the spermogonia and aecidia is especially 

 abundant and conspicuous. It is found in all of the leaf tissues, 

 but is most abundant in the mesophyll near the lower epidermis. 

 Most of the hyphae have their axis of growth in the long axis of 

 the leaf. They are almost entirely intercellular except for the 

 haustoria, which are short, knoblike, and usually penetrate only a 

 short distance into the host cell. The hyphae are somewhat irregu- 

 larly septate. The individual cells vary considerably in size. The 

 average breadth is about 5 ju and the length three or four times the 

 breadth. A single globular nucleus is located, usually, near the 

 center of the cell; its diameter is but slightly less than the short 

 diameter of the cell. The small nucleole stains a ruby red and is 

 readily seen. The chromatin stains a deep blue and is distributed 

 in small globular masses that are connected by delicate strands. 



