An Encyclopedia of Horticulture. 



249 



Fki. 320. Ciitoi'P OF Spores of Pi'ccinia graminis— a, Uredo- 

 spores, formed in early summer ; (, Teleutospore, fonueil later 

 in the season ; st. Stalks supporting the Spores. 



and they are most often developed only in late summer. 

 They grow on erect footstalks or branches, to which they 

 usually remain long united, and they are considerably 

 thicker-walled and darker than the others, from which 

 also they differ in form (see Fig. 320). They may be 

 one-ceUed {Vromyces), two-celled (Puccinia and Gijmno- 

 sporan/iium), or three- or more-celled (Trij)/iraj/?m«m 

 and Plirarjmidium). The teleutospores, for the mo.st 

 part, rem.ain for a considerable time without germinating, 

 often continuing unchanged all winter. On germinating 



Pnccinia — continued. 

 aecidiospores. Like the latter, they germinate almost 

 at once, and push their mycelium into the tissues of the 

 host-plant through the stomata. 



3. The Teleutospore (from teleutaiii, final, and spora; I 

 so called because it is the final form in the cycle) is 

 sometimes called the Pucciniospore ; but this name is less 

 suitable, as other genera besides Pucciiiia produce such 

 spores. These are. in most cases, produced on the same 

 substratum as the nredospores, but later in the season ; 



Fig. 321. Puccinia graminis— Teleutospore germinating and pro- 

 ducing Sporidia (fip) on tips of small stalks {st) ; pi\ Mycelium 

 Tube growing out of the Spore. 



(see Fig. 321), a mycelium tube is pushed out from each 

 cell, or only from one. These tubes often become 

 divided near the tip, by cross walls, into a row of cells, 

 from each of which a small branch arises, and bears, at 

 its tip, a small, rounded or oval body, called a sporidium. 

 The sporidia produce a new mycelium, which penetrates 

 into suitable host-plants, and frequently gives rise to 

 fficidia in them. Occasionally, two forms of teleuto- 

 spores occur in the same Fungus, e.g., one-celled and 

 two-celled in Puccinia nii.vfa. In most of the species, the 

 cycle is not so complete as the above ; and, in fact, it 

 has been traced, as yet, in but few species. As has 

 already been said, most cryptogamic botanists believe 

 that some of the species live, during part of the cycle, on 

 one food-plant, and during the other part on another. 

 Such species are said to be heteroecious (from heteros, 

 different, and oikos, a home). Those that live on a single 

 food-plant during the whole cycle are said to be aut- 

 CDcious (from auto.'f. the same, and oikos). 



Pnccinia is readily distinguished, in the perfect con- 

 dition, from other genera of Ureilinew by the teleuto- 

 spores being free from one another and two-celled ; or, at 

 least, there are two-celled spores, associated, in a few 

 species, with three- or more-celled abnormal exceptions, 

 or with a one-celled form, much like the teleutospores 

 of the allied genus Uromyces. The two-celled spores 

 vary in length of stalks, in forms, and in surface- 

 markings of the cells, &c. ; and on these characters we 

 must depend for distinguishing the species. The genus, 

 in the systems in most frequent use on the Continent, 

 is broken up into sections differing from one another in 

 the compIetenes.s of the cycle, so far as known, and in 

 other minor peculiarities. 



Vol. IIL 



Pnccinia — continued. 



Owing to the parasitic habit of the very numerous 

 species included in the genus, there are few genera of 

 Fungi more directly injurious ; and a considerable number 

 grow on and damage garden and field produce. The 

 injurious effects are due, in some cases, to the abstrac- 

 tion of nourishment by the mycelium of the Fungus from 

 the food-cells of the plant, and to the injury done to 

 the epidermis by the spore-masses tearing it off the 

 tissues beneath. These tissues, in consequence, cease 

 to do their part in supplying food to the plant. In a 

 smaller number of cases, the plant is stimulated by the 

 Fungus to a local over-production of diseased cellular 

 tissue. This is peculiarly the case in the a;cidinm stage, 

 e.j;., on Barberry, on Gooseberry, and on Mints. In some 

 oases, plants may suffer extremely, and may even be 

 killed tty tlie Fungi {e.g.. P. Malracenntm almost ex- 

 tirpated Hollyhocks in many districts a few years ago), 

 or, if not killed, may be much distorted by them ; e.g.. 

 Mints attacked by the ajcidium of P. Mentha;, Anemones 

 bearing P. Anemones, &c. In many cases, the plants 

 are simply weakened, without marked distortion ; e.g., 

 cereals affected badly by the red and black rusts 

 {P. graminis and P. straniinis), and Onions overgrown 

 by P. nii.vtn. Some do not seem to injure very greatly 

 the plants affected by them, but this is exceptional. 

 Their growth and distribution are favoured by moisture, 

 which promotes the formation and germination of the 

 spores. 



Remedies. As usual with internal parasites, no cure 

 is known for plants, or parts of plants, attacked by these 

 Fungi ; hence, remedies must be directed to the preven- 

 tion of the spread of disease. This is best accomplished 

 by the removal and destruction of the infested struc- 

 tures, where thi.s is possible. Where the attack is very 

 serious, e.g., in the case of Hollyhocks and of Onions, 

 it is good policy to sacrifice the entire crop, if neces- 

 sary, to preserve that of the following year from infec- 

 tion. As already said, moisture favours the distribution 

 of the Fungi, and the soil should, therefore, be well 

 drained. Lastly, where the hurtful Fungi are believed 

 to be hetercEcious, it is well to remove the supposed 

 intermediate host-plant ; e.g., in the ease of Puccinia 

 graininis of cereals and other grasses, which is believed 

 to live on Barberry-bushes as JEcidium Berberidis. the 

 Barberries should be removed from the neighbourhood 

 of the fields. Yet too much reliance must not be placed 

 on this method, as these Fungi are known to thrive when 

 restricted to the one food-plant. 



In the following enumeration of the species of Puccinia 

 falling under the observation of gardeners, those of 

 which only teleutospores are known are tir.st mentioned, 

 and afterwards those of a more complex nature. 



1. P. Bu.n often forms dark, warty spots, in large 

 numbers, on leaves of Box. Teleutospores alone are 

 known. They are brown, smooth, and oblong or club- 

 shaped. The Box does not, as a rule, seriously suffer. 



2. P. Mtdvac^arum is only too well known to most 

 gardeners, because of its ravages on Hollyhocks, Mal- 

 lows, and allied plants. For an account of the appear- 

 ances pS*oduced, of the liistory of the Fungus, and of 

 the injury done by it, see Hollyhock Fungus. Only 

 teleutospores are known. They are jialo brown, smooth, 

 and pointed at both ends. The plants suffering from 

 the growth of this Fungus seldom recover, and often die 

 in a short time. 



3. P. Arenarice belongs to the same group, having, 

 so far as is known, only teleutospores ; these are pale 

 yellowish-brown, and slender. They form small, brown 

 masses, often in irregularly - concentric groups, on the 

 leaves of Pinks, and of many wild, as well as garden, 

 Caryophyllaceous plants ; but, unless the Fungus is 

 very abundant, the host-plant is seldom endangered by 

 its growth. 



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