June 1, 1891.] 



KNOWLEDGE 



109 



not been produced as the result of the union of male and 

 female elements. They have simply been cut off, one by 

 one, from the ends of the hyphse, and have surrounded 

 themselves with a thick wall as a protective covering ; but, 

 like spores, they are capable of germinating and producing 

 a mycelium exactly similar to that which gave them origin. 

 The wind catches them and carries them from blade to 

 blade of the wheat. Having alighted thereon, germination 

 commences. A small tube is sent out from each gonidium ; 

 it pierces the cuticle or outer coating of the leaf-surface, 

 and insinuates itself between the cells of that body. It pro- 

 bably effects its entrance nito the leaf by secreting a 

 ferment which dissolves the hard cuticle. This fermenta- 

 tion is exhibited by many fungi. It enables many of them 

 to penetrate into the hard wood of trees. When the tube 

 has reached the interior of the leaf, it germinates, and 

 the product of germination is a mycslium like that of its 

 parent. On this gonidia may again arise. Two or three 

 generations of gonidia may be produced in this way in a 

 single summer. 



The fungus at this stage was formerly called I'l-i'ilu 

 lincdiis, and its gonidia are still known as ' irihi-iidiiiilid. 



The blade of wheat is a transitory structure, it does 

 not live all winter, but the mycelium of the fungus could 

 not survive that period without a means of sustenance. 

 In point of fact, its existence as such terminates with that 

 of the life of its host ; but it makes provision for the con- 

 tinuance of the species, to the cost of the poor farmer on 

 whose lauds it has settled. 



Towards the end of -July the brownish pustules we have 

 previously referred to assume a black appearance, and 

 become more prominent. Now, microscopic examination 

 reveals a curious fact. Where previously uredo-gonidia 

 existed, two-celled bodies with very thick walls have ap- 

 peared (Fig. 11. (I., t.i/.). On some isolated stalks a uredo- 



Fio. II. — a. Transversp section of Wheat-blade through collection 

 of Teleuto-gonidia (ad. nat.); t.;/., telcuto-gonidia ; m., mycolium. 

 (JFuch magnified.) //. Tclouto-gonidium (ad. nat.) (Very much 

 mngniticd.) r. Dingrammatic representation of germination of 

 tolouto-gonitlium (I. g.); />. in., promycelium ; i/., promycolinl 

 gonidia. 



gonidium may still be visible. Tlioso are also gonidia, but 

 by reason of their structure are better fitted to withstand 

 the rigors of winter than those produced in the earlier 

 part of the season. They are the last gonidia to appear 

 on the niycelimn, so they have received the name of tclcuto- 

 gonidia (tcXcutos " last "). 



All this time the fungus has been preying upon its host, 

 and preventing the elaboration of sap for the building up 

 of its seeds. Its attacks are thus dreaded by the farmer. 

 This stage of the fungus, which was not known until 

 recently to have any connection w'ith the preceding, re- 

 ceived the name of Puccinin ijniiiiinia. 



The mildew, or blight, was known as far back as the 

 time of Shakespeare. In AV;;// Lear, Act III. so. iv., we 

 read that " the foul fiend Flibbertigibbet mildews the 

 white wheat." " The fungoid nature of the mildew was not 

 known, however, until the latter half of the last century, 

 for TuU, writing in ITHH, attributes it to the attack of 

 small insects, ' brought (some think) by the east wind,' 

 which feed upon the wheat, leaving their excreta as 

 black spots upon the straw, ' as is shown by the micro- 

 scope.' ! " ■■ 



The teleuto-gonidia remain on the decayed leaves all 

 winter, but in the spring they throw oft" their dormant 

 state, become active, and germinate. Each di\nsion sends 

 out a small tubular body (Fig. II. r.,p.iii.) which divides 

 up into three or four cells that still retain organic connec- 

 tion with one another. From each cell is thrown out a 

 short process, whose tip develops into a minute bulbous 

 swelling (Fig. II. c, //.). The two tubes produced from 

 the teleuto-gonidia are called promycelia, and the swellings 

 just mentioned the promycelial gonidia. These last are 

 produced in immense numbers, and are carried about by 

 the wind. 



It was noticed many years ago that in the vicinity of 

 Barberry bushes (lierhrriK vulijiiris) the wheat in a wheat- 

 field presented the rustfil appearance which we now know 

 to be due to the presence of teleuto-gonidia, while in 

 neighbouring parts the wheat retained its normal appear- 

 ance. Many accomits were given of the connection 

 between the Barberry and mildew on wheat, but no one 

 knew why this connection should exist. So convinced 

 were farmers of the harmful nature of the Barberry that 

 almost all these bushes have been uprooted from our 

 hedges ; and in 1760 an Act was passed in Massachusetts 

 enforcing the destruction of these apparently harmless 

 shrubs. 



The promycelial gonidia, one would naturally imagine, 

 would germinate on the wheat-leaves, but experience tells 

 us that this does not take place. They will only develop 

 when they fall on the Barberry, or its ally the Mulmnia 

 ilu-ifoUa. In the leaves of the former plant, and in 

 addition on the berries of the latter, they develop a myce- 

 lium in no way diftering from that seen in the leaves of 

 the wheat. The hyphie or threads of the thallus insinuate 

 themselves between the cells, and absorb nourishment 

 from them. Its presence on the Barlierry would probably 

 have passed unnoticed were it not that during the early 

 summer reproductive cells arise from the mycelium. Then 

 it is seen that the under surface of the leaves are infected 

 here and there with circular yellow blotches. The aid of 

 a pocket-magnifier shows each blotch to be composed of 

 a zone of small holes, from which a yellow powder issues. 

 On the upper side of the leaves minute apertures are 

 present, arranged likewise in a circular manner. If we 

 examine a section of the leaf under the microscope, the 

 yellow patches will show themselves to be composed of 

 cup-shaped bodies. livery cup is tilled with bright yellow 

 cells (Fig. 111.. ". .V'-) arranged in linear series, and each 

 series arises from the down- turned end of a hypha. A 

 distinct wall surrounds each cup or tn-idiniii (Fig. III., <i.), 



Plowright. /iiiVisA Crediiiea- and Ustilai/inea. p. 47 



