168 MINNESOTA BOTANICAL STUDIES. 



Fig. 17. Effect of sulphuric acid on cell wall and pits; a, pith 

 cells treated for ten to fifteen minutes in 50 per cent, solution ; b, 

 pits as seen twenty-four hours after treating the section with the acid. 

 The walls have been entirely dissolved, x 300. 



Fig. 1 8. Cluster of filaments, x 300. 



Fig. 19. Longitudinal section through a cystocarp. x 85. 



Fig. 20. Group of spores from cystocarp with thin-walled cells 

 separating them, x 300. 



Fig. 21 . Longitudinal section through the pericarp : #, cortex; b, 

 pith ; <:, spores, x 300. 



Fig. 22. Longitudinal section through an infested cystocarp. The 

 upper left-hand portion sho\vs the manner in which the parasite pene- 

 trates the host, x 56. 



Fig. 23. Portion of the same region enlarged showing to the left 

 the tissues of the host pericarp and to the right the long filamentous 

 cells of the parasite, x 300. 



Fig. 24. Section through frond producing nemathecia. On the 

 upper surface is a mature nemathecium, on the lower surface two 

 two younger ones : <z, gelatinous cuticle ; b. pore-like break in cuticle ; 

 c, cortex cells; d^ cells from which tetraspores are produced; e, para- 

 site ; f, pith filaments, x 300. 



