318 BOTANT. 



perennial, the fungus reappearing year after year upon tlie 

 same stems, or upon the new stems grown from the same 

 roots ; in annuals it must obtain a foothold in the young 

 plants as they grow in the spring. 



409. — The mycelium can be traced in the Monocotyle- 

 dons often for long distances ; thus in the smut of Indian corn 

 ( Ustilago Maydis), at the time the spores are found in the 

 distorted grains the hyphffi have been detected at all inter- 

 mediate points down to the lower internodes, and in the 

 smut on wheat ( Ustilago carlo) they have been observed in 

 every part of the plant, from the root through the stem to 

 the iniiorescence. In neither case, however, are the hyphae 

 to be found in parts through which it is not necessary for 

 them to pass in order to reach the point where the spores 

 are formed ; thus they are usually not found in the leaves 

 unless spores are formed in them. 



410. — The formation of spores appears to have some re- 

 lation to the development of the host plant, as they form 

 only in certain parts of the latter, and are not produced 

 until the growth of these parts has taken place. Thus in 

 the Bunt of wheat {Tilletia caries) the spores are formed 

 only in the young ovaries ; in the anther smut of the ;S^t- 

 lenece ( Ustilago antherarum) the spores are formed in the 

 young anthers ; in one of the smuts of the sedges ( Ustilago 

 urceoloriim) they form on the upper surface of the ovary, and 

 in the smut of wheat, oats, etc., in the young flowers. In 

 cases like these it is evident that the time of spore-forma- 

 tion is dependent upon the development of the flowers of 

 their host ; and if these are earlier or later in their appear- 

 ance, the spore-formation will vary accordingly. In the 

 smut of Indian corn ( Ustilago Maydis), on the other hand, 

 the spore-formation may take place in other parts of the 

 plant, as well as in the ovary ; thus it not infrequently makes 

 its appearance upon the stems, and even upon the leaves. In 

 Ustilago hypogcea the spores are produced underground 

 upon the root of the host plant {Linaria spuria), and in 

 Ustilago marina, in the tissues of Scirpus parvulus. under 

 water ; with these two exceptions, the spore-formation always 

 takes place in parts above ground. 



