STEVENS: DISEASES OF GRASSES. I27 



superstition. A section of one of these masses just forming on a leaf 

 sheath is shown in fig. i, plate XIII. It will be seen that the mass 

 is an outgrowth of the tissues of the sheath, in which the parasite is 

 already forming its masses of dark spores. The new growth is of 

 great advantage to the fungus, since the latter can proceed with its 

 development only in newly formed cells. A movement of elaborated 

 sap must set in toward the new region of growth, and the fungus uses 

 these favorable conditions to branch out rapidly and produce its spore 

 masses. In the figure (i, plate XIII) the new growth is seen to have taken 

 place between two primary bundles ; the secondary bundles between 

 them have been pushed upward by the abnormal enlargement and 

 distortion of the cells beneath them, and have become centers for the 

 outgrowth of irregular tracheids extending fitfully into the newly 

 formed tissues. The new outgrowth consists chiefly of thin-walled 

 cells containing starch grains in abundance. The outer cells, which 

 are a continuation of the cuticle of the sheath, are elongate and com- 

 paratively thin-walled. As the spores mature, the surrounding tissues 

 become compacted and ruptured, allowing the penetration of moisture 

 and the consequent further swelling and bursting of the mass. In the 

 somewhat distorted cells beneath the new growth, and to some dis- 

 tance laterally, the ramification of the mycelium can be distinctly 

 made out. Brefeld has shown by his extensive experiments that the 

 germ tube of the smut spores can penetrate the nascent tissues of any 

 part of the plant, and -is not restricted to the root node of the young 

 seedling, as was formerly supposed. He states as his belief, that if 

 the germ tube which enters at the root node does not develop rapidly 

 enough to get into and keep pace with the growing point, that its fur- 

 ther ascent in the plant is impossible. Indeed, his careful experi- 

 ments, many times repeated, seem to prove that in the case of the 

 rapidly-growing corn plant, those smut masses which appear on the 

 ovaries or staminate flowers were produced by the inoculation of the 

 inflorescence just as, or before it burst from its sheath. Once estab- 

 lished in the host, the fungus has the power of irritating the tissues 

 wherein it lies, into an abnormal growth, and in the new growing 

 point thus established, it completes its development. 



The mycelium of a fungus may penetrate the cells of its host either 

 through openings already formed, or by piercing the cell membrane 

 mechanically, or, the cell membrane may be dissolved by the secretion 

 of some ferment by the growing point. The figures on page 124 repre- 

 sent cells from the sheath of a corn leaf sectioned through a smut 

 outgrowth. Thin places or perforations often occur in the cell walls, 

 as shown in figs. 3 and 6, and the mycelium sometimes penetrates 

 at such places ; but more frequently it seems to pass through the cell 



