X98 



HARDWICKE'S SCIENCE-GOSSIP. 



Ill III idi III, but it is now known that this necidium is 

 the early state of a puccinia (/'. magiiiisiana) upon 

 the common reed. 



The bare enumeration of these experiments would 

 be wearisome to the general reader, but a ievr 

 remarks upon th e structure and physiology of the ure- 

 dines generally, will probably not be uninteresting. 



It has long been known that ihe genus Puccinia has 

 two forms of fruit, the uredo spores, and the teleuto- 

 s|X)res ; that the former are produced in great abun- 

 dance, and that they germinate with great freedom, 

 as soon as they are mature, and that the teleutospores 

 (puccinia) do not germinate until after a longer or 

 shorter period of rest. It lias more recently been 

 shown, that when the germinating teleutospores are 

 placed upon a healthy specimen of the proper host- 

 plant, in many instances instead of producing the 

 uredo, they produce an recidium ! and that when the 

 spores of this necidium are sown upon a healthy leaf 

 of the host-plant instead of reproducing the a'cidium, 

 they give rise to the uredo. So that we must regard 

 the rccidium, the uredo, and the puccinia as different 

 forms of the same fungus, although our predecessors 

 looked upon them as being distinct genera. A 

 perfect puccinia is one which has all three states, as 

 for example the species so common upon Epilolniiin 

 hirsutuiii (P. (pilobii). In this fungus the Kcidium 

 occurs first in spring : then the uredo, and with it, 

 but a little later, the teleutospores (puccinia). In this 

 instance all three forms occur in succession upon the 

 same host-plant. But a puccinia may have all three 

 spore forms, and yet they may not all occur upon the 

 same plant, as for example the Puccinia graiuinis, 

 the wlieat mildew. In this the uredo and teleuto- 

 spores grow upon wheat and various grasses, but the 

 acidium is confined to the barberry. As this species 

 is verj' common and well-known, its physiology will 

 be given more freely, as it may be taken as the type 

 of the genus. It must, however, be incidentally re- 

 marked that all puccinia; are not perfect, inasmuch 

 as they do not possess all these three spore-forms. 

 For example, some have the aecidium and puccinia 

 forms only, as P. aneiiioiics, P. on the common wood 

 anemone. Others have uredo and puccinia only, and 

 no ivcidium as far as is at present known, as /'. p-n- 

 upriim, on the garden plum. Lastly, there is an 

 interesting group in which both the acidium and uredo 

 forms arc wanting, but in which the teleutospores 

 germinate at once, without a period of rest, as in the 

 hollyhock disease, P. iiialvaccarum ; P. arenaria: is 

 another instance of this last-mentioned group. 



The earliest state of Puccinia sraniiuis is the 

 xcidium state, well-known to microscopists, from its 

 attractive appearance under a low magnifying power. 

 An axidium, or clu^ter cup, is, as its name implies, a 

 cup-hke structure, full of spores, usually yellow 

 though sometimes white. These spores are produced 

 in chams, or necklaces, from the bottom of the cup • 

 they are usually globose, and when placed in a damp 



atmosphere readily germinate by throwing out a germ 

 tube. The cup itself arises from an entanglement of 

 hyaline tubes (the mycelium) ramifying amongst the 

 cells of the host-plant. If a ripe jecidium spore be 

 placed upon the cuticle of the plant, upon which it is 

 destined to complete the course of its existence, it 

 will throw out a germ tube. This germ tube travels 

 over the leaf until it comes to a stoma, into which 

 its extremity is insinuated, and thus the secidium gains 

 entrance into its host. Once inside, the germ tube is 

 in its proper soil ; it luxuriates, and in a few days pro- 

 duces mycelium. This new mycelium exists in the 

 substance of the leaf for from eight to twenty days 

 before manifesting its presence externally. At the 

 end of this period, it does so at first, by producing a 

 sickly yellow spot, which is very soon the place 

 where a mass of spores (uredo spores) are formed, 

 underneath the entitle at first, but very soon, as they 

 grow, rupturing it. These uredo spores are not like 

 the aecidium spores, formed in chains, but are pro- 

 duced singly, one from a separate branch of the 

 mycelium. If a young specimen of uredo be examined 

 many of the spores will be seen to have attached to 

 them a little piece of the mycelial tube from which 

 they were produced, in this state they constitute the 

 old genus Trichobasis. 



The uredo spores vary in shape, in size, and in 

 colour in various species, but they all have this in 

 common that they germinate within a short time of 

 their maturity, but if kept for a week or two they 

 lose this power. When they are placed on a leaf of 

 their proper host-plant they throw out germ tubes, in 

 the same manner as the recidium spores do, which 

 like them enter through the stomata and form my- 

 celium inside the host-plant. This mycelium in from 

 ten to twenty days reproduces the uredo. It might 

 be thought that as the Eecidiuru spore produced a 

 uredo, a uredo spore would produce an aecidium, 

 but this is never the case. The function of the uredo 

 spore is to reproduce itself and disseminate the fungus 

 to which it belongs with great rapidity. The rust of 

 wheat is the uredo state of the mildew fungus. But 

 the uredo spore has this disadvantage, it does not 

 retain its power of germination for any length of time. 

 The same mycelium which in spring and summer has 

 been actively producing uredo spores, towards autumn 

 in point of time, but in reality dependent upon the 

 maturity of the host-plant, produces another and very 

 different form of spore, the teleutospore^ or puccinia. 

 Now these teleutospores or puccinia spores are very 

 much larger than the uredo spores, and instead of being 

 like them simple are two-celled. The puccinia spores 

 are as a rule firmly fixed to the host-plant which bears 

 them. They are too large to be readily diffused liy 

 atmospheric agencies. They are typically resting 

 spores — they do not germinate as a rule until the 

 following spring, but lie in a state of quiescence un- 

 changed as the host-plant decays. When sjDring 

 comes and fresh leaves of their host-plant appear, they 



