202 THE PRINCIPLES OF FLORICULTURE 



From a small enlargement, the oogonium develops into a 

 thick-walled, colorless body, which is shut off from the mycelial 

 strand by partition walls. A rounded mass of granular proto- 

 plasm separates from the cell wall, and forms a more or less 

 solid body in the center. This is surrounded by a clear fluid 

 called the periplasm. Thus the egg or female organ becomes 

 ready for fecundation. 



A stalked antheridium is formed from a section of the same 

 mycelial thread which bears the oogonium, by a partition wall 

 cutting off an elongated cell. This is the male cell. One end 

 comes in contact with the wall of the oogonium ; the whole cell 

 swells, and the end thus in contact puts out a slender tube which 

 pierces the oogonium, extends through the periplasm, and 

 discharges its contents or sperms into the oogonium contents. 

 This fecundated cell now becomes the egg, and in this stage, the 

 fungus may rest for a considerable time. The oogonium is always 

 formed within the cell structure of the host, and is only liber- 

 ated by decay of the stem, and the rupture of the wall of the 

 oospore. 



174. Ecology of " damping-off " disease. Some of the condi- 

 tions favoring the development of the pathogen are a close, 

 humid atmosphere about the seedlings or cuttings; over-water- 

 ing of plants, especially at night ; seedlings weakened because 

 of insufficient air, food or light ; the seed-pan insufficiently filled 

 with soil to bring seedlings high enough for perfect ventilation 

 about the base of the stems, and seedlings too thickly planted. 



175. Preventives. The " damping-off " fungus may in a 

 measure be prevented by sterilizing the soil for a few hours 

 before sowing seeds or transplanting seedlings ; using fresh sand 

 in cutting benches ; using plenty of sand in soil to insure perfect 

 drainage ; giving seedlings plenty of light and ventilation to 

 insure a strong, vigorous growth. Apply water in the morning, 

 and do not over-water. 



176. Remedies. To assist in overcoming the fungus, stir 

 the surface soil and keep the temperature low. If plants are 

 large enough, transplant at once into soil which is free from 

 spores. Sprinkling with warm sand may serve to check the 

 spread of the fungus. 



177. Mycomycetes. This great group comprises the Asco- 

 mycetes (Sac fungi), which are the principal fungi attacking 

 greenhouse plants ; also the Uredineae, Basidiomycetes and 

 what are called Fungi Imperfecti (those in which some of the 

 stages are unknown). 



178. Rose mildew. Classification: Perisporiacese. Sphcero- 



