110 



KNOWLEDGE 



[June 1, 1891. 



j:«p 



and, like the spores, it is connected with a mycelium in the 



centre of the leaf. The arrangement of the sBcidia in 



groups has caused them to be called cluster-cups. The 



mycelium is connected towards the upper surface of the leaf 



with oval-shaped bodies, spermagonia (Fig. III. s.), whose 



openings to the exterior are the small 



apertures before-mentioned. They 



contain rod-shaped cells, the so-called 



spermatia (Fig. III., sp.). 



As in the previous stages, this 



phase of the life-history of the fungus 



was not known to have connection 



with any of the others, and had a 



_ gg_j|-, V name of its own — .Kdilium hcrheridis. 



„ „, _ It now remains to determine the 



Fig. III.^ — Transverse . . , ,. ,, .. 



section of leaf of Bar- ongm and use of these respective 



berry (Berherii vul- parts. The Aphis, or plant-louse, has 



yan's), showing fccidium the peculiar power, possessed, how- 



■(«!.), with ^cidiospores g^g^^ ^^ ^^jj^j. jQ^^jy animals, of pro- 



iTuKi.withTp'ermTtia ducing numerous successive broods of 

 (sp.). young from unfertilized eggs, ibis 



is called parthenogenesis (-n-ap^evos 

 "avirgin"; and ■yciTau " to reproduce"). On the prothallus* 

 of the Fern antheridia and archegonia may be developed, 

 but from the ovum, or egg, in one of the latter a young 

 fern-plant may arise without union with a spermatozoid ; 

 nay, further, without even the production of an ovum a 

 fern-plant may be developed on it. As it is usual for 

 fertilization to take place, these abnormal developments are 

 termed apdijanunts (otto " from " ; and ya/itu) " to marry "). 

 In a group of Fungi allied to that (.lu-ididmijcetes) to which 

 Puccinia belongs, viz. in the Lichens, spermatia are de- 

 veloped. One fertilizes a female organ, find the result nf 

 their union is ii cup-shaped hadij reri/ niurh like the cecidiuui eif 

 Au'idiiun herheridis. No female organ has been found on 

 this fungus, so it is argued that apogamy here takes place. 

 As the yellow cells germinate and produce a mycelium, 

 and as they have resulted from tbe union of male and 

 female elements, they are called spores, in contradistinc- 

 tion to the asexually-produced reproductive cells, gonidia. 

 It was believed until lately that the so-called spermatia 

 were male cells, which were now functionless on accoimt 

 of apogamy always happening in .V.eiiliuin herheridis ; but 

 this view of their nature must now be cast aside, for Prof. 

 Plowright has succeeded in causing these to germinate. 

 Their true nature at the present time is unknown. 



The inability of the promycelial gonidia to germinate 

 on the blades of Wheat is a matter of wonderment, but 

 the same peculiarity is displayed by the spores [lecidin- 

 sjiores) found in the recidia, or cups of the Berberis. They 

 will germinate only when they reach a blade of Wheat, 

 and not on the Berberis leaf from which their parent 

 mycelium derived its sustenance. Their germination pre- 

 sents features akin to that of the uredo-gonidia and teleuto- 

 gouidia. A tube is sent out, which in this case, however, 

 enters the wheat-blade by way of a stoma. In the in- 

 terior of the leaf it branches and produces a mycelium, 

 on which uredo-gonidia are produced. 



We have thus arrived at the stage of the life-history 

 with which our description commenced. This fungus then 

 passes part of its existence on one plant and part on 

 another, and is parasitic on both. It is thus said to be 

 metoxenous (//.era " change" ; and t'evos a " guest ") ; or, in 

 other words, to change its host. The term hetercecism 

 (Irepos" other," and oiVos " a house ") is also used in connec- 



* For explanation of terms see article on " A Seed, and what it 

 Contains," Knowledge, April 1891. 



tion with it, implying that it effects a change of residence 

 during the course of its life. The diagram (Fig. IV.) will 



oecT.tt\um 



Fig. IV. — Life-cycle diagram of Puccinia graminis. As the uredo- 

 mycelium produce uredo-gonidia, which again produce a mycelium 

 like the parent, the life-cycle is at this stage lengthened, while on the 

 other side apogamy causes shortening of the cycle. 



serve to make clear the wanderings and vicissitudes of 

 this lowly organism. 



It must not be imagined that all Fimgi have such a 

 complicated life-history. In many cases it is very simple. 

 Moreover, all are not parasitic ; some are saprophytes. 

 They live, like the mushroom, on dead organic matter, 

 which originally was built up by living beings. 



Notices of Boolts. 



Sofip Bulihles and the Farces ndtich mould them. By Prof. 

 C. V. Boys, F.E.S. (Society for Promoting Christian 

 Knowledge.) — This very fascinating little book is calculated 

 to start old people as well as young in a course of experi- 

 menting for themselves. It is written in very popular 

 language, being the substance of three lectures delivered 

 to a juvenile audience in the Theatre of the London Insti- 

 tution. Prof. Boys is a very accomplished experimenter, 

 with a happy gift of devising simple mechanical con- 

 trivances to illustrate his meaning. Those who were not 

 fortunate enough to hear the lectures will find ample wood- 

 cuts and other illustrations to make the meaning clear, 

 and at the end of the book Prof. Boys has given a series 

 of practical hints as to bubble-blowing and making some 

 of the simple apparatus which he used. The importance 

 can hardly be overrated of inducing young people to 

 experiment for themselves. It teaches them to observe 

 and to reason for themselves, and is a very important 

 adjunct to the training of the memory which is now too 

 exclusively looked upon as education. Possibly in some 

 cases Prof. Boys has been a little too daring in his attempts 

 at explanation. Thus, in trying to explain that the section 

 of a film between two parallel discs is a catenary when 

 the pressure on the inside is equal to the pressure on 

 the outside, he shows his child audience the sections of 

 a cone by throwing the shadow of a Hat candlestick on the 

 wall, and then tells them that he will trace a catenary 

 by rolling upon a straight edge a piece of board, cut 

 into the form of a parabola, letting a piece of chalk, at its 

 focus, trace the catenary on the black-board. But with a 



