134 PEACTICAL BOTANY. 



If the Cress cultures be kept damp for some days 

 longer, a thick felt of hyphse will be formed, which will 

 bind the seedlings together : and finally the disorganisa- 

 tion, which usually begins near the base of the hypo- 

 cotyledonary stem, will spread throughout the seedlings, 

 causing complete rotting. 



II. Mount part of a stem of one of the collapsed 

 seedlings in water, and examine under a low power : 

 observe 



1. That the tissues show an abnormal appearance at 

 the point of curvature, their colour is yellowish, and 

 the individual cells show signs of having lost their 

 turgidity. 



2. That numerous colourless branched hyphae extend 

 along the surface of the seedling, being most numerous 

 at the point of curvature, and less frequent further 

 up. 



III. Tease out a portion of the infected part, as well 

 as of the healthy part above, with needles in water, 

 and mount so that a part at least of the epidermis 

 shall be seen in external surface view ; or sections may 

 be cut, the infected part being held between pieces of 

 pith : in such preparations observe 



1. The healthy part of the epidermis with elongated 

 cells, and occasional stomata. 



2. The branched, highly refractive, and for the most 

 part non-septate hyphae, running with an irregular, 

 but mostly longitudinal course along the outer 

 surface. 



3. Mark especially the points of entry of the Fungus 

 into the host-plant : this may be either 



a. By perforation of the outer wall of a cell of the 



