SCIENCE-GOSSIP. 



221 



examined under the microscope, it will be seen 

 to consist of myriads of rounded yellow grains 

 (fig. 2 ys), not unlike grains of pollen. These 

 grains are spores, and are known technically as 

 " uredospores," since they cause a scorched or 

 shrivelled appearance on the wheat plants. 



As time passes on it will be noticed that the 



Fig. 3. — Transverse section through a portion of an infected 

 stem, at a later stage than tig. 2 (magnified), e, Ruptured 

 epidermis; r s, "Rusty '' teleutospores ; c. Cells of tissue of 

 stem, with interwoven filaments. 



number of yellow patches does not sensibly in- 

 crease, but that those already present begin to 

 change their colour, becoming brownish or red. 

 It is this brownish red dust which causes the well- 

 known rusty appearance on the wheat. Microscopic 

 examination will show that this rust is composed 

 also of spores, darker in colour and of totally 

 different shape to the uredospores. These " teleuto- 

 spores," or later-formed spores, are more or less 

 diamond-shaped, and divided into two parts, or 

 cells. (Fig. 3 rs and fig. 4.) 



To trace the cause of the appearance of these 

 .two kinds of spore, recourse must be had to the 



Fig. 4.— Teleutospores from fig. 3 (highly magnified). 



microscope. If thin, transverse slices or sections 

 of the stem be cut through one of the yellow 

 patches and examined carefully, a number of cells 

 will be seen more or less closely compacted 



together, and bounded by a layer one cell thick, 

 called the "epidermis," making up together the tissue 

 of the stem. In certain places the epidermis will 

 be seen to be ruptured, and at these spots the 

 yellow spores will be seen each at the end of a 

 minute hair or filament. The filaments may be 

 traced back into the tissue of the stem, where they 

 form a branching network between the cells. By 

 examining sections cut at various stages, it will 

 soon be made clear that the rusty teleutospores are 

 produced at the ends of the same filaments, thus 

 proving that the two kinds of spore are due to the 

 same cause. 



The filaments which thus ramify in the tissue of 

 the stem are those of a minute and lowly organised 

 plant or fungus, which takes up its abode in the 

 wheat plant, and robs this, its host, of its food 



Fig. 5. — Transverse section of portion of an infected 

 barberry leaf (magnified), c, Epidermis of upper surface; 

 1' >, Epidermis of lower surface ; a, Cup-shaped depression, 

 filled with recidiospores ; s, Spermogonium ; t, Tissue of leaf. 



supply. Such a lowly-organised plant living at 

 the expense of a higher one is called a " parasite." 

 The earlier- formed yellow spores will, if the 

 conditions of warmth and moisture be favourable 

 readily germinate on a fresh wheat plant, and it is 

 by the transference of these yellow spores from an 

 infected plant to a healthy one, that the disease 

 spreads in the early summer ; and it is interesting 

 to notice that the infection has been known to 

 spread in lines whose direction coincides with that 

 in which the wind has been blowing. 



All efforts to make the dark teleutospores 

 germinate on the wheat plant have failed, and 

 for a long time the subsequent history of these 

 spores was enshrouded in mystery. 



It had been pointed out as long ago as the year 

 1736, that the proximity of barberry bushes to 

 cornfields apparently had some connection with 

 the appearance of rust. In the State of 



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