INJURIES INDUCED BY PLANTS 



6l 



roundish haustoria. The consequence is that the starch- 

 grains soon disappear, and the protoplasm dies and contracts- 

 from the cell-walls (Fig. 15, a). While the fungus continues to 

 spread in the plant, numerous hyphae break through the epidermis 

 to become sporangiophores (Fig. 16). The swelling of the ex- 

 tremity (Fig. i6,/) gives 

 rise to a lemon-shaped 

 sporangium, which is pro- 

 vided with a papilla at the 

 apex, and a short pedicel 

 at the base (Fig. 16, g). 

 After its abscission from 

 the stalk the latter elon- 

 gates afresh to produce a 

 second sporangium (Fig. 

 1 6, g, h\ and meanwhile 

 the first generally drops 

 off (Fig. 1 6, z). Should 

 the sporangia come into 

 contact with water as, for 

 instance, a drop of rain 

 or dew which has lodged 

 about the cotyledons 

 they germinate directly, 

 putting forth one or more 

 germ-tubes, which gener- 

 ally proceed to bore into 

 the epidermis of the host- 

 plant. In other cases the 

 protoplasmic contents of 



C 



FIG. 1 6. Epidermis of a diseased cotyledon 

 of the beech, a, the external wall of an 

 epidermal cell ; b, the cuticle ; c, a hypha, 

 which has intruded itself between the wair 

 and the cuticle ; at d it pushes up the latter ; 

 at e it appears on the surface, and at f it 

 forms a sporangiophore. After producing 

 the first sporangium it branches at g, to 

 form a second h, while the first drops off 

 at i ; a stoma is shown at k from which 



the Sporangium form a sporangiophores project. 



large numberof extremely 



'minute and very active gonidia (swarm-spores, or zoospores 

 Fig. 17, c\ which are capable of free movement after the apex 

 of the sporangium has been dissolved. For some hours these 

 swim about in a drop of rain with all the activity of infusoria, 

 until they settle on the epidermis of the host-plant, when they 

 germinate with one or even four tubes (Fig. 17, a, b). Some- 

 times the zoospores germinate in the interior of the sporangium 



