158 



IHK A(ii;ieULTUHAL NKWt 



May U, 1910. 



FUNGUS NOTES. 



THE CHIEF 



OF FUNGI. 



GROUPS 



Part VI. 

 The UEEDiNALES (continued). In order to present a clear 

 account of tlie different stages in the life-history of these 

 fungi, a description of a particular species, Puccinta 

 ffvainhiis, the black rust of wheat and other cereal crops, will 

 be given. The spring condition of this fungus 

 occurs on the leaves and other parts of the 

 barberry (Hcrheris i<ulc/aris), and on allied 

 species; this is the stage already referred to as 

 the cluster-cup, or aecidiuni stage. It consists 

 of clusters of minute cup-shaped structures 

 with white, fringed margins and golden yellow 

 centres. The yellow colour is due to the forma- 

 tion of masses of spherical golden-brown 

 spore.s, which are produced in chains from 

 the ends of hyphae arranged in parallel layers 

 at the bottom of the cups. With this stage 

 are associated very minute spores known as 

 spermagonia, which are abstricted from the 

 tips of long, fine hyphae produced in flask- 

 shaped cavities or concejitoc/es on the under 

 side of the leaves. According to one theory, 

 these spermagonia were originally male repro- 

 ductive cells, but have now lost their function. 

 This is, however, uncertain, and very little 

 is really known about them, beyond the fact 

 that they have practically lost their power of 

 germination. The ripe aecidiospores are scatt- 

 ered by the wind, and if they-fall on the surface 

 of a leaf of wheat or other suitable grass 

 plant, they germinate; the: germ-tube enters 

 the leaf through a stoma, grows rapidly and 

 infects an area around the stoma. The 

 mycelium then gives rise to uredosjMres, 

 borne in a mass, which burst through the 

 tissues of the host and form rusty brown 

 st^-eaks on the leaves. The uredospores are 

 oval structures, uuicelluLar, brown in co'.our, 

 and covered with spines. They germinate 

 almost immediately, when ripe, putting out Flu. "26. Pucci 

 several germ-tubes through pores arranged on Germinating 



the central line round 

 the spore. These spores 

 can infect other wheat 

 plants, and their object 

 is to increase the num- 

 bers of the fungus dur- 

 ing any one season. As 

 the season proceeds, the 

 rust streaks liecome 

 darker in colour, owing 

 to the formation of the 

 third spore-stage, the 

 teleiitoKj'ores. These are 

 produced from the same 

 mycelium as the uredo- 

 spores, and are at first 

 often rai.xed with them, 

 though later the pu.s- 

 tules contain teleuto- 

 spores only. These 

 spores are more or less 

 oval in shape, dark 



brown in colour and bicellular, with a marked constriction at 

 the median wall. They have thick walls, and are intended 

 to carry the fungus through the winter. They either fall to 

 the ground, or remain, on the withered leaves of the grass, in 

 the pustules in which they were originally produced. In the 

 spring, they germinate, each cell giving rise, through a single 

 pore, to a four-celled basidium, as is shown in Fig. 26. Each 

 cell of the basidium then produces a short sterigma, on the 

 top of which the last spore-form, a sporidium, is borne. 

 This spore is a hyaline, unicellular, frequently 

 oval structure, much smaller than the other 

 spore-foims; it is carried by the wind to the 

 leaves of the barberry, where it germinates, 

 enters the leaf, and produces a mycelium giving 

 rise 'to the cluster-cups again, thus completing 

 the life cycle. The necessity for two different 

 hosfplants on which to complete the life-cycle 

 is known as haieroicism. This phenomenon was 

 first defini'ely demonstrated by Schooler in 

 lS18,by infecting rye from the barberry,and was 

 subsequently confirmed by de Barj' and others. 

 It was, however, suspected as early as 1781, 

 when a law was passed in the State of 

 Massachusetts, compelling the destruction of 

 all barberry plants in the neighbourhood of 

 fields of wheat and rye. 



To summarize, there are four spore-stages 

 in the life history of most of the Uredinales : 

 the uredospore, the teleutospore, the sporidium, 

 and the aecidiospore. Of these, the first two 

 occur on one host plant, as for example, wheat; 

 the sporidia are produced from the teleuto- 

 spores lying on the ground or elsewhere, and 

 can, ,only infect a different host plant, as for 

 example, barberry; from the inycelium so 

 formed, arise the aecidiospores, which can only 

 infect the first host. The phenomenon of 

 heteroecism is general among these fungi, but 

 is not always necessarj-, as some species can 

 produce all their spore-forms on the same host. 

 The two remaining groups of the Basidio- 

 mycetes— the Hymenomycetesand the Gastero- 

 mycetes — possess one character in common 

 NIA Geamini.s. besides the undivided basidia, for in both the 

 Teleuto.spores. basidia are closely packed together, side by side, 



Fig. 27. Itoox i)jsEASK nv Sui:ai!- 

 CANE. {Mm-asmms mrchari.) 



to form a definite 

 layer known as the 

 hymenium. The 

 ditterence between 

 the two groups lies 

 in the fact that, in 

 the Hymenomy- 

 cetes, the hymenium 

 is exposed from the 

 first, while in the 

 Gasteromycetes it is 

 enclosed until matu-' 

 rity. 



The HYMENOMY- 



LETES. This group 

 may be divided 

 into four subdivis- 

 ions: — i: 



Agaricacea^. 



Polyporaceae. 



Hydnaceae. 



Thelephoraceae. 



Fn:. 28. I'AUA.'iiricWouxD Fungus 

 {Poli/porus sp.) 



