Rensselaer Union, Volume 8, Number 3, Rensselaer, Jasper County, 7 October 1875 — How the Rust Grows. [ARTICLE]

How the Rust Grows.

The transformations in the growth of a Dutterfly are so evident that the merest school boy may try the experiment and observe the truth of it for himself; but in the rust the objects are so very small that the changes can only be seen by the keen eyes of skilled observers, aided by the best powers of the microscope. Beginning with the spores of the mature rustplant, as seen in the black stains on the old stubble of any grain field, it will be found that when the warm and moist days of spring come these spores germinate, producing in a few days a short stem bearing a crop of other spores of very much smaller size. To avoid confusion, these must be called by their scientific name, sporidia , while the parent spores arb the ieleutospores. The sporidia have never been seen or made to grow upon the grain; but when they find their way to the leaves of a barberry bush they soon begin to germinate, and make themselves manifest on the under surface of the leaves in what ate commonly known as “cluster-cups.” The interior of' these pretty little cups is closely packed with spores of a still different kind, styled the secidium spores. These will not grow upon the barberry, but when they fall upon a blade or stalk of grain they soon produce the yellow, rusty covering so often seen as the grain is beginning to ripen, and caused by a multitude of u~edo spores. Later in the season this uredo state produces the final perfect teleutospores, thus completing the circuit of life in this little rust-plant. Long before this rust was discovered to be a plant farmers had noticed that there was a close relation between it and the barberry, and at present the latter is being rapidly destroyed with good results, though it can scarcely be expected that the rustplant will thereby become extinct, as probably the secidium state grows on other than the barberry, though not yet discovered elsewhere. This is an excellent illustration of polymorphism, so common among fungi, and "it also answers well to show the vast number of spores these microscopic plants produce. The teleutospore usually bears from five to ten sporidia, and allowing that only one of these finds the barberry leaf there may he from one to fifty cluster-cups as the result. In our case suppose only one , and a low estimate, for its contents would be 250,000 secidium spores, and if only one in a thousand finds a place on the grain-stalk ■and each brings forth its 250,000 fold there would be under such circumstances 62,500,000 spores from the single one with which we started. Taking the same teleutospore, and supposing every spore in all the stages found its place to fill it, the result would be 1,602,500,000,000,000,000 spores, which may be looked upon as its true descendants for the season. Or, giving each inhabitant of the globe his equal share of these reproductive bodies, he would have nearly as many as there are individuals in the whole human race. This may seem like a very large story about a very small matter, but it is not the only strange truth the microscope has revealed. —Scribner for October.