174 BOTANY. 



produce spores in great abundance, which burst through 

 the epidermis. There is a still greater simplicity of struc- 

 ture in the plants of the present order than in the Rusts, 

 probably due to a greater degradation through excessive 

 parasitism. 



359. The parasitic threads of the Smuts are well defined, 

 and consist of thick-walled, jointed, and branching fila- 

 ments, which are generally of very irregular shape. They 

 grow in the intercellular spaces and cell-cavities of their 

 hosts, and send out suckers (haustoria), which penetrate 

 the adjacent cells much as in the Mildews. The para- 

 site generally begins its growth when the host-plant is 

 quite young, and grows with it, spreading into its branches 

 as they form, until it reaches the place of spore-formation. 

 In perennial plants the parasite is perennial, reappearing 

 year after year upon the same stems, or upon the new 

 stems grown from the same roots; in annuals it must ob- 

 tain a foothold in the young plants as they grow in the 

 spring. 



360. The life-history of the Smuts has not yet been com- 

 pletely made out. Two kinds of spores have been observed 

 in certain species, but neither the sexual organs (if any 

 exist) nor the mode of entrance of any of the species into 

 their hosts has yet been discovered. 



361. The Smut of Indian corn (Ustilago maidis) is very 

 common in autumn. The parasitic filaments are found in 

 various parts of the host, and at last those which reach the 

 young kernels become semi-gelatinous and form spores in- 

 ternally. There is much crowding and distortion of these 

 spore-bearing filaments, but here and there their resem- 

 blance to spore-sacs is quite evident (Fig. 96). When the 

 spores are ripe, the gelatinous walls of the spore-sacs, dis- 



