The Arizona sentinel., 1886-06-26
POTATO ROT.
The Tiny Parasitic Plant Which Causes
 This Disease.

 The Tiny Parasitic Plant Which Causes
 This Disease.
 Prof. J. H. Ponton, of the Ontario Agricultural College, in an article on this subject, writes: This disease has re- ceived a great deal of attention from botanists since the days when it became a scourge in Ireland and other parts of the British Isles, and it is now conceded to be the result of a minute fungus called phytopthora infestans. This at- tacks all parts of the plant-leaf, stem and tubes. By those ignorant of the life history of this tiny parasitic plant little attention is paid to its appearance on the tops, and no alarm is experi- enced until the potatoes are affected. But being very contagious, its presence on the leaves should become a serious matter, especially when we remember that it spreads with great rapidlty. it is usually indicated by the tops pre- senting a blotched, brownish, spot ted, dead appearance. A close ex- animation of the potatoes showing this will discover innumerable slender stems growing up out of the surface of the leaves and stems of the affected plants. These branch and swell out at the ends into pear-shaped minute bodies (spores), which are produced by millions. When ripe they separate from the stem and, being exceedingly light, pass into the atmosphere, where they are waited about, many of them finally reaching the ground or settling upon plants. Un- der favorable conditions of moisture and heat the contents of microscopic spore may push out long, minute tube, which can penetrate into any part of the potato plant and give rise to the fungus; or may separate into several distinct portions (swarm spores), which burst through the spore wall and be- come the source of the parasitic plant The mature plant which lives in the tops and tubers is very minute, and can be seen only by the ald of the micro- scope. It consists of many colorless, branching, thread-like structures. These penetrate the tissues of the potato and feed upon the juices, so that it soon weakens and begins to waste away. From the thread-like structures tiny stalks arise, assuming beautiful plant-like forms and bearing upon their branches the spores already referred to. They live but short time, but the thread-like structure is perennial and hardy, and from fragments of it new fungi may arise. It is said by some that another kind of spore is produced which can winter, and thus give rise to the organ ism in another season. These are the so-called resting spores, apparently for the purpose of keeping the species over certain periods, while the spores already considered are produced rapidly SO as to hasten the spread of the fungus under favorable conditions. This minute microscopic plant is certainly low form of vegetable life, incapable of manufacturing food from the mineral kingdom, but fastening upon other plants and feeding upon their juices. A wet season supplies conditions well adapted for it's development, and hence we find the ''rot' associated with such weather. There is no doubt that many spores are always more or less present, but they are prevented from being a source of trouble because the weather is not suited for their growth. Chicago Tunes.