128 



THE GARDENER'S ASSISTANT. 



the spores formed on the Pear or Hawthorn can 

 alone infect the Juniper; hence the remedy is 

 in this case easy; remove from the neighbour- 

 hood one of the two host-plants, and the fungus 

 cannot continue to produce itself. The two 

 host-plants may be growing quite half a mile 

 apart, the minute spores being conveyed from 

 one to the other by wind, insects, or birds. 

 If it is not desirable to remove either of the 

 host-plants, no pains should be spared to find 

 the diseased Juniper, which can readily be 

 recognized by the swollen diseased part of 

 the branch being covered with the conspicu- 

 ous yellow fungus. The diseased branch 

 should be removed, as the mycelium of the 

 fungus is perennial in the diseased spot, and 

 produces a crop of spores every spring. Many 

 other very destructive fungi also require two 

 host-plants, among Avhich may be mentioned 

 Wheat-rust or Mildew. The mildew stage 

 proves very destructive to Wheat and other 

 cereals, whereas the second or cluster-cup 

 stage of the same fungus grows on living 

 leaves of the common Barberry. 



The very common disease of seedlings, 

 known as damping off, is caused by a minute 

 fungus called Pythium de-baryanum, a very 

 primitive type of parasite and a typical 

 example of those simple aquatic forms which 

 possess many points in common with the alga3, 

 from which the fungi originated as a special- 

 ized branch of organisms in the first instance. 



"Damping off" sometimes assumes the 

 form of a serious epidemic in seed-beds, seed- 

 lings of various kinds, also the prothalli of 

 ferns, being destroyed wholesale when grow- 

 ing in damp and shaded situations. 



The fungi causing this form of disease are 1 

 so exceedingly minute that they are entirely 

 invisible to the naked eye, and the first indi- 

 cation of their presence is the wilting and falling 

 over of the seedlings attacked. If a seedling 

 that has fallen over is carefully removed from 

 the soil, the collar or portion of the stem just 

 above the ground-line Will, on examination, pre- 

 sent a shrivelled appearance, and if examined 

 under a microscope, the hyphae and fruit of the 

 fungus will be seen emerging from the tissues 

 of the seedling. 



When once present the disease usually spreads 

 rapidly, destroying all the seedlings within a 

 few days. But this can only occur when the 

 ground is constantly more or less saturated with 

 water. When a seed-bed is infected with the 

 fungus it must not be used for the same pur- 

 pose again until the soil has been thoroughly 



sterilized by the use of quicklime or soot, and 

 exposure to the air. 



As illustrations of higher forms of the group 

 of fungi to which Pythium belongs — the Phyco- 

 mycetes — may be mentioned the Vine Mildew 

 (Peronospora viticola) and the well-known Potato 

 disease (Phytophthora infestans). The summer 



Fiar. lriti.— Vine Mildew (Peronospora viticola). 

 Summer form of fungus on grapes (natural size). 2. Summer fruit (magni- 

 fied 80). 3, 4, 5. Detached spores of summer fruit (magnified 350). 6. Winter 

 form of fruit formed on the mycelium of the fungus present in the tissues 

 of the diseased portion of the plant (magnified 350). 



form of fruit of these fungi is an exceed- 

 ingly delicate white mildew on the surface of 

 living leaves, the conidia as usual being pro- 

 duced rapidly and in immense numbers, thus 

 enabling the disease to spread quickly to ad- 

 joining plants. In the case of the Vine, winter 

 fruit is also produced in large numbers in 

 the tissues of diseased and fallen leaves, and 

 unless all such are removed and destroyed 

 there is the danger, or almost certainty, of a 

 recurrence of the disease the following season. 

 Winter fruit is not produced by the fungus 

 causing the Potato disease, but on the other 

 hand the mycelium of the fungus passes from 

 the diseased stems into the tubers, where it 

 extends and passes into the young stems and 



