Laffekty — Disease of Cultivated Flax. 25.3 



permeated with mycelium, and is killed. Such dead seeds eventually become 

 covered externally with conidia, and, as a rule, remain adherent to the inner 

 walls of the fruit. 



If the seeds are more nearly ripe before infection of the fruit occiTrs, the 

 fungus, as before, reaches the two outer layers of the seed-coat, but does not 

 penetrate the third or fibrous layer, Hence the embryo remains secure 

 from attack, and its subsequent development proceeds normally. Although 

 unable to gain entrance to the embryo, the fungus often continues to spread 

 in the outer layers of the seed coat, and produces conidiophores and conidia 

 on the surface of the seed. 



As the infected seeds become ripe they break away from the placenta, 

 and the fungus produces conidiophores and conidia in great abundance on 

 the resulting scar. Slightly affected seeds show the presence of conidia only 

 at or in the region of the hilum. 



3. Details of the Fungus. —Whew portions of affected plants, whether 

 stems, leaves, sepals, or fruits, are kept for forty-eight hours or so in a moist 

 atmosphere, minute beehive-shaped pustules {acervidi), scarcely visible to 

 the naked eye, are produced on and around the margins of the discoloured 

 diseased areas. 



These acervuli, which occur, as a rule, directly over the stomata, are 

 gelatinous in consistency and hyaline to milky in appearance. They are 

 made up of large numbers of conidia, produced by groups of conidiophores, 

 the swollen tips of which emerge only slightly through the stomata. One 

 such conidiophore emerging on the surface of a diseased leaf and producing 

 conidia is shown in Plate X, fig. 5. 



Occasionally on diseased stems and branches, especially when the disease 

 has advanced to a very considerable extent, cases are met with where masses 

 of conidia are to be found in minute pockets beneath the epidermis, as well 

 as on its surface. These submerged conidia are produced by conidiophores 

 which at first produced conidia in the sub-stomatal respiratory cavity. 

 Eventually, however, owing to the pressure from beneath, the epidermis 

 bursts, and the conidia are forced out in bulk. Conidia have never been 

 observed to be extruded through a stoma in the form of a tendril, as takes 

 place commonly in the case of a pycnidium with an ostiole. This submerged 

 production of conidia has never been observed on leaves, and, though some- 

 times seen on stems and branches, it is not the usual method. In the 

 majority of cases conidia are produced outside of the host. 



The acervuli have been examined carefully in all stages of development, 

 and on all parts of the host plant for the presence of setae, but the latter 

 have never been met with. 



