2110 Journal of Applied Microscopy 



of a living room. A little too much heat interferes with the germination just 

 as much as a like decrease in temperature. 



In winter the culture should be kept either in a greenhouse or where the 

 temperature can be kept constant by means of a thermostat. In the summer 

 the experiments are usually more successful if the cultures are made in the 

 evening. Under ordinary, favorable conditions the usual amount of growth 

 will be reached in an average time of about 24 hours. 



Very little need be said about the use of the microscope in the study of 

 these cultures. A good combination for ordinary study is the No. 6 eye- 

 piece and the 4 mm. objective. This will sometimes be found inconvenient, 

 however, in making drawings with the camera lucida attachment, and in such 

 cases it may be found more convenient to use a 16 mm. objective with an eye- 

 piece of comparatively high power. Of course, a general survey of the culture 

 should first be made with a lower combination, such as a 1(5 mm. objective with 

 eyepiece No. 4 or No. 6. 



Selection of Material. There are five well known spore forms of the rust 

 fungi, (1) spermatia, (2) aecidiospores, (3) uredospores, (4) teleutospores, (5) 

 sporidia, the last named being developed directly from the teleutospores. In 

 addition to these, another distinct spore form occurs in the species Pticcinia 

 vexans Farl. and has been described by the writer and called ainphispore. 

 This form, however, is extremely rare, but is believed by Dr. J- C. Arthur 

 to occur in at least one other species. 



A few hints may well be given here as to the selection of the material 

 among these different forms for germination studies. Until recent years it 

 was not supposed that the spermatia produced regular germ tubes, but that 

 the germination is always simply a process of budding. Dr. N. A. Cobb 

 and the writer have shown, however, that ordinary germ tubes are produced 

 in the germination of these spores as well as in the other spore forms. These 

 observations make it probable that the so-called budding process simply 

 represents instances where the germ tubes have soon ceased their growth in 

 length, and, swelling somewhat in the middle, have given themselves the form 

 of buds. However, it is possible that actual budding occurs. Among the 

 species that have been found by the writer to be particularly good for studying 

 the spermatia, are the rust of blackberry, Aecidium cenothem Mont.* on Oiiagra 

 biennis^ the ordinary apple leaf rust, and the barberry rust. In the first named 

 species, especially, the spermatia are comparatively large and are readily 

 germinated. Spermatia, though germinating readily in w^ater, will be found 

 to do much better in a rather dilute sugar solution, or perhaps still better in 

 a solution of honey. 



The beginner often finds difficulty in germinating ajcidiospores which, 

 I think, is usually because the material does not occur in sufficient abund- 

 ance, so that in collecting the specimens they cannot be kept fresh for 

 so long a time as if there were more material to draw from. Some of 



*Not to be confused with Ae. peckii, De Toni, which has recently been shown by Dr. W. 

 A. Kellerman to be connected with a Puccinia on Carcx trichocarpa, Jour. Myc. 8 : 20, May. 

 1902. 



