The Tylostomaceae of North America 



Bv V. S. White 

 (With Plates 31-40) 



The members of this family arepuffball-like plants, which form 

 underground in the shape of rounded masses, appearing at first on 

 the mycelium as minute thickenings, and gradually reaching their 

 full development. The ball has a thick outer covering, and an 

 inner, and usually thinner one, commonly known as the peridium 

 proper. The upper and larger portion of the ball is composed of 

 sporogenous tissue, and there is a lower sterile portion which elon- 

 gates when conditions are most favorable, forcing the upper portion 

 up through the surface of the ground, and consequently rupturing 

 the outer coat which originally enveloped the whole mass. In 

 some genera this outer coat remains at the base as a distinct cup- 

 like volva, the upper portion then being carried up almost intact 

 and falling away or adhering to the peridium ; in other cases the 

 outer coat is ruptured irregularly, bearing very slight traces at the 

 base of the stem or even none at all, and in the genus Tylostoina 

 this coat adheres more or less to the peridium, nearly always leaving 

 some traces in the form of a collar at its base. The stem is com- 

 monly of a firm, almost woody texture, and the plants can be quite 

 satisfactorily preserved in a dry condition. They vary greatly as 

 to size and shape, but are all constructed on the same general plan, 

 having a more or less irregularly globose peridium, and a distinct 

 footstalk, which is usually, though not always, more than twice 

 the length of the peridium in mature forms. The methods of 



[Issued 27 August.] 421 



