104 MASSACHUSETTS HORTICULTIRAL SOCIETY. 



species has quite a wide range, the Srlerotinia lihevtinia F'kl,, 

 which we know in this country as frequently producing diseases 

 of forcing-house plants, causing decay of the stems, and then 

 developing small black bodies of fungus tissue called sclerotia. 



Tendency toward the Exclusion or Forms from the 

 Life Cycle. — Another peculiarity in the tendency of certain 

 fungi is that of the exclusion, or shutting out of forms, or stages 

 from its life history. A good illustration of one of these fungi 

 is seen in a sterile fungus Avhich I have frequently found to be 

 the cause of damping off of seedling plants, it being often a more 

 common agent in the production of this disease than the PijtMum 

 deharyanum, which has often been spoken of as the sole cause of 

 this trouble. I speak of it as a sterile fungus because in my 

 experience with it during several years from several different 

 states, I have never been able to find or to produce in artificial 

 cultures any recognized fruiting form. According to pecu.liari- 

 ties of its development it would be classed by some under the 

 form genus Rhizomorplia, when it develops slender rope-like 

 strands by the parallel interlacing of its threads, or under the 

 form genus ScleroHum, when it develops these characteristic 

 bodies. 



It is enabled to propagate itself by the breaking up of short 

 moniliform threads on the surface of the sclerotium, the sepa- 

 rated segments of two or more cells functioning as conidia, 

 while the sclerotia act as resting bodies to tide the fungus over 

 unfavorable periods for its growth. We cannot say that it has 

 no other form in nature, and probably some form of true fructi- 

 fication is developed at some time, though this is not necessary. 

 As compared with many other forms which quite regularly 

 develop their characteristic fructification, there is a very decided 

 tendency here to the loss of that form if that has not already 

 taken place. The plant at one time undoubtedly had a fruiting 

 form. It may by this time have lost it, or it may have become 

 so changed that in this vegetative condition it practically repre- 

 sents, either biologically or structurally, an entirely different 

 species from its immediate ancestor, and thus has no comple- 

 mental fruiting form into which it could pass in order to complete 

 its development. 



Some rhizomorphs, it is true, have been found to be vegetative 

 states of some member of the mushroom family, the so-called 



