9o 



DISEASES OF CULTIVATED PLANTS 



Seedling cabbage disease ( Olpidium brassicae, Dang.) often 

 causes devastation in beds of seedling cabbages ; the injury 

 comes from the gardener's point of view under the category 

 of ' damping off.' The tender cells of the young stem are 

 attacked by the fungus, soon the plant droops, falls down, and 

 dies. 



Sporangia, solitary or several in each cell of the host, the 

 long slender tube from which the zoospores escape often 

 passes through a layer of four or five cells to reach the 

 surface of the host-plant. Zoospores i-ciliate, globose. 

 Resting-spores tinged yellow, warted. 



FlG. 17. Olpidium brassicae. 1, zoosporangia 

 in cells of cabbage leaf; 2, zoospores; 3, resting- 

 spores. All highly mag. 



From a scientific standpoint this fungus should be recog- 

 nised from the similar effects produced by Pythium de barya- 

 num (Hesse), although the practical preventive measures apply 

 equally to both pests. 



Plenty of sunlight, and absence of excess of moisture in 

 soil and air are the only practical remedies. Where the 

 disease has shown itself is an indication that the locality is too 

 dam]). 



Woronin, Pringsh. Jahrb. (1878), p. 557- 



Olpidium lemnae (Schrdt.). This parasite is met with in 

 the epidermal cells of the duckweed (Lem/ia minor). 



Xoosporangia globose, with a long beak, 18-20 /1 diam.. 

 resting-spores globose, almost colourless, 12 20 /< diam. 



