75 



all directions between its cells, from the epidermis to the pith, 

 in the tissues of the leaves, and in the seed vessels. These 

 filaments are long narrow tubes capable of rapid growth and 

 elongation (Fig. I. a), able to push their way between the cells 

 of any of the tissues and are much branched. They never divide 

 up by transverse walls except at the points where reproductive 

 organs are formed, these being always cut off completely from the 

 remainder of the filament. We may, therefore, speak of them as 

 simple cells. Such a mass of fungal filaments, whether found 

 inside a plant or outside is spoken of as a mycelium, and the 

 individual filaments are called hyphse. 



The hyphaj contain a considerable quantity of protoplasm, 

 which forms a thick parietal layer on the walls, enclosing a 

 central cavity, across which numerous thick protoplasmic strands 

 pass. In some places, however, they appear to be quite full of 

 protoplasm, with no central cavity, and it is probable that at 

 these points i-apid growth and elongation are taking place. 

 Nuclei are found in large numbers in the protoplasm in all parts 

 of the mycelium, both in the parietal layer and in the central 

 strands (Fig. I. n), but in those places mentioned above, where 

 the hyphse appear to be completely full of protoplasm, the number 

 of nuclei present is considerably increased, and they foi'm a not 

 inconsiderable portion of the contents of the hyphse. In other 

 places, however, the nuclei are comparatively few in number, and 

 are scattered here and there, often at considerable intervals, in 

 the protoplasm. 



The hyphse obtain their nourishment from the host-plant through 

 a large number of short globular expansions which are formed 

 laterally on the hyphse, and penetrate into the interior of the cells 

 of the host (Fig. I. 6), whence they absorb the food substances 

 required and transmit them to the filaments, where they are used 

 up in furthering the growth and development of the fungus. 

 These structures are known as haustoria, and may be developed 

 anywhere on a hypha. They are often developed in whorls 

 consisting of as many as five or six, or even more, radiating 

 from the hypha in a very regular manner. They vary con- 

 siderably in size, and sometimes almost completely fill the cells 

 into which they penetrate ; they are also often lobed or branched, 

 and they always contain a large quantity of protoplasm and 

 numerous nuclei, which have passed into them from the filament. 



