12 Diseases of Truck Crops 



out a germ tube, or as is more generally the case, by 

 the outer wall dissolving and the inner mass breaking 

 up into small bits of naked protoplasm known as 

 zoospores. Most fungi have two spore stages, the 

 summer form intended for rapid dissemination and 

 spread, the winter form intended to carry it over 

 through cold or any other unfavorable weather con- 

 ditions. The term conidia is applied to all spore 

 forms borne free on special fruiting stalks known 

 as conidiophores (fig. 2 a). A pycnidium is a sac- 

 like body (fig. 2 m) in which are borne the summer 

 spores. A perithecium is a sac-like body (fig. 2 1) 

 which bears the winter spores of certain fungi. 

 Other terms here used in describing parts of fungi 

 will be found in the glossary. 



NATURE AND FUNCTION OF A HEALTHY SOIL FLORA 



The function of a normal soil is to provide avail- 

 able plant food. About 95 per cent, of the com- 

 bustible weight of a growing plant is made up of 

 carbon, hydrogen, and oxygen and nitrogen. The 

 remaining 5 per cent, constitutes the mineral or the 

 ash of the plant. Carbon, hydrogen, and oxygen are 

 taken in the form of carbonic acid and water ; nitrogen 

 from nitrates produced by bacteria out of organic 

 matter of the soil. The ash or the mineral elements 

 of the plant are taken directly from the soil. Neither 

 the organic nor the mineral elements are in a form 

 which plants can make use of until they have been 

 acted on by certain definite organisms in the soil. 



