DISEASE OF TIIK CARNATION. 



1-21) 



fungus is most commonly seen upon the older leaves, but it is by no 

 means rare to find the younger and more vigorous leaves attacked as 

 well as the leaves and nodes of the flowering stem. 



On the diseased areas, on both sides of the leaf, numerous small 

 black pycnidia are present, plainly visible to the naked eye, and from 

 these the spores escape by means of an apical pore. The pycnidia 

 (fig. 115) vary in size, some measuring 200 n x 140//. They are embedded 

 in the leaf, being formed in the respiratory cavity below a stoma, and are 

 at first spherical, but as they mature they become flask-shaped ; the 

 apical pore then projects above the epidermis. The peridium of the 



Fig. 115.— Longitudinal section of a leaf of Carnation with pycnidium of Septoria 

 Dianthi. The epidermis is not shown. Zeiss Obj. D, Oc. 4, naniilin sect. 



pycnidia is black, and composed of a layer of two or three cells in thick- 

 ness, and immediately inside the peridium is a series of short parallel 

 hyph;e from which the spores are abstricted. The pycnidia have been 

 observed at all seasons of the year. 



The spores (fig. 116) are colourless and very long, 32 fi x 4*8 /u when 

 measured in water directly after issuing from the pycnidia, straight or 

 slightly curved, and sometimes divided by a transverse septum. They 

 issue from the pycnidia as a viscid mass, and are rapidly dispersed in 

 water. The spores germinated readily in a hanging drop or on nutrient 

 gelatine, protruding a long germ-tube. I have also followed the germina- 

 tion upon a Carnation leaf. 



When the spore is sown in a drop of water on a young and vigorous 

 Carnation leaf still attached to the plant, the germ-tube is similarly 

 protruded, and has been observed to enter the leaf through a stoma. 

 Fig. 116 represents a few cells of the epidermis stripped from a leaf twenty- 

 four hours after sowing. The spore has germinated and the germ-tube is 

 seen entering the leaf through a stoma. At the spot where the spores 

 are sown, the discolouration due to the action of the hyphaj becomes 

 apparent in about fourteen days, and gradually spreads in all directions, 

 but more especially towards the apex of the leaf. Sections across the 



