256 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Boston duriug the spring. Most of the work to be described was 

 done on this form, but ^cidia on Hoastonla ccendea^ Ranunculus sep- 

 tentrionalis, Anemone neinorosa, and Sainbacus Canadensis, were also 

 studied. Peridermium elatinum on Abies balsaineu, and Roestelia lacerata 

 on the fruit of Amelanchier Canadensis., were also examined, and some 

 particulars regarding the later stages of the a;cidium seen in the other 

 species wei'e confirmed. 



In all the work the methods of manipulation employed w^ere the 

 familiar ones. Sections were made both free-hand and with the 

 microtome. With the microtome sections the material was stained 

 either in toto or on the slide ; Delafield's hajmatoxylin being found 

 most favorable for the former, while for the latter and also for the 

 hand sections eosin, Hofmauu's blue, or Mayer's acid ha^malum 

 was used. Lactic acid was usually employed instead of potash for 

 distending and clearing the sections, because it does not disorganize 

 and render so exceedingly transparent the tangled masses of hyphaj 

 as does the latter. Most of the actual work of examination and 

 almost all of the drawings were made while the sections were still in 

 aqueous media, for any method of mounting soon renders the speci- 

 mens so transparent that it is impossible to see the details. For final 

 mounting, glycerine was usually preferred to balsam, although for the 

 study of the nuclei specimens stained with ha^matoxylin and mounted 

 in the latter were found the best. As is usual in the studying of 

 structures of this sort, where certain^ differentiated portions must be 

 disengaged from tangled masses of filaments, it was found that a toler- 

 ably thick section, properly dissected and macerated, was often more 

 instructive than even a complete series of thinner ones. 



^CIDIDM ON PeLTANDRA. 



This form, which is the oecidium of Uromyces Caladii, being the one 

 which was most thoroughly worked up, will be taken up first, to be 

 followed by a discussion of the other forms named. The first material 

 used for this examination was collected by Professor Thaxter, who 

 kindly placed it at my disposal ; quantities of the same ajcidium have 

 been collected by myself several times since, and the material killed in 

 both picric and chromic acids. In selecting the portions of the plant 

 for sectioning, petioles were usually taken, as they were easier to cut 

 and also contained less chlorophyll than the leaves. By taking pieces 

 of considerable length and cutting longitudinal sections the young 

 aecidia could be traced with ease. 



