366 REPORT OF THE COMMISSIONER OF AGRICULTURE. 
finally ruptures. These conceptacles are visible to the naked eye, 
appearing as very minute black points on the surface of the spots. © 
They are not abundant, and often there are many spots, called sterile, 
entirely without them. ‘The spores are difficult of artificial germi- 
oo and no results were attained by sowing them upon healthy 
eaves. 
Possibly there is some genetic connection between the Macrospo- 
rium and the Phyllosticta. ‘This has been suggested as.a probability, 
but the studies we were able to make afforded us no opportunity to 
form even an opinion on this question. 
Where a few trees of catalpa are grown especially for shade or 
ornament it may be possible to preserve their foliage from this dis- 
ease by the application (preventive) of some fungicide, but no ex- 
periments have yet been made with this end in view. 
10.—BLACK-SPOT ON ROSE LEAVES. 
Actinonema rose. 
(Plates VIII and IX. ) 
(a) GENERAL OBSERVATIONS. 
There are several parasitic fungi that produce black spots upon : 
the leaves of our cultivated roses ; but the most common and inju- 
rious, and the one to which we generally refer in speaking of the 
“leaf spot,” is that known to mycologists as Actinonema rose. It 
was named Asteroma rose by Libert as early as 1826, and afterwards 
transferred to the genus Actinonema by Fries. It is also called 
Asteroma radiosum. The nature of the disease has been studied and 
described by Frank and Eriksson, and Sorauer describes it in detail 
in the second edition of his work on “‘ Diseases of Plants.” 
The disease is very wide-spread, occurring in nearly all the coun- 
tries of Europe as well as in the United States. Here it is quite 
universal, although there are local areas apparently free from it. 
(b) EXTERNAL CHARACTERS. 
Late in the spring, or early in the summer, the disease makes its 
appearance in the form of round or irregularly-shaped black spots 
upon the upper surface of the living leaves. Generally only the full- 
grown leaves are attacked, and those within three or four inches of 
the branches seem to be healthy. . 
The spots are small at first, but as the disease progresses they in- 
crease in size, and may become half an inch in diameter. Often a 
number of them coalesce, and in severe attacks the leaf is nearly 
covered with large dark patches. 
From the beginning the spots are fringed at the edges, and 
although the form is frequently irregular at first, they usually become 
distinctly circular later, especially on the smooth-leaved varieties. 
In the latter part of the season the spots grow light colored and dry 
in the center, showing that that part of the leaf is entirely dead, and 
by this time, if not before, the discoloration penetrates through the 
leaf and appears on its under side. 
The moss roses and those with thick rough leaves, seem to suffer 
more than other kinds, but there are few, if any, that are invulner- 
