July 26, 1888] 



NA TURE 



299 



following. A few years ago Wolff showed that if the spores 

 from the sEcidia of Peridermium Pini (var. acicold) are 

 sown on the leaf of Senecio, the germinal hyphae which 

 grow out from the spores enter the stotnata of the Senecio 

 leaf, and there develop into the fungus called Colcosporium 

 Senecionis. In other words, the fungus growing in the 

 cortex of the pine, and that parasitic on the leaves of the 

 groundsel and its allies, are one and the same : it spends 

 part of its life on the tree and the other part on the herb. 



If I left the matter stated only in this bald manner, it is 

 probable that few of my readers would believe the wonder. 

 But, as a matter of fact, this phenomenon, on the one hand, 

 is by no means a solitary instance, for we know many of 

 these fungi which require two host-plants in order to 

 complete their life-history ; and, on the other hand, several 

 observers of the highest rank have repeated Wolff's experi- 

 ment and found his results correct. Hartig, for instance, 

 to whose indefatigable and ingenious researches we owe 

 most that is known of the disease caused by the Perider- 

 Jiiium, has confirmed Wolff's results. 



It was to the brilliant researches of the late Prof. 

 De Bary that we owe the first recognition of this re- 

 markable phenomenon of hetercecism — i.e. the inhabiting 



Fig. 35. — A spore of Feridertiiiuvt Pini germinating. It puts forth the 

 long, branched germinal hyphae on the damp surface of a leaf of 

 Senecio, and one of the branches enters a stoma, and forms a mycelium 

 in the leaf: after some time, the mycelium gives rise to the uredospores 

 and teleutospores of Colcosporinm Senecionis. (After Tulasne : highly 

 magnified.) 



more than one host — of the fungi. De Bary proved that 

 the old idea of the farmer, that the rust is very apt to 

 appear on wheat growing in the neighbourhood of 

 berberry-bushes, was no fable ; but, on the contrary, that 

 the yellow sEcidium on the berberry is a phase in the 

 life-history of the fungus causing the wheat-rust. Many 

 other cases are now known, e.g. the /Ecidium abietinum, 

 on the spruce firs in the Alps, passes the other part of its 

 life on the Rhododendrons of the same region. Another 

 well-known example is that of the fungus Gymno- 

 jporangium, which injures the wood of junipers : Oersted 

 first proved that the other part of its life is spent on the 

 leaves of certain Rosaceas, and his discovery has been 

 repeatedly confirmed. I have myself observed the follow- 

 ing confirmation of this. The stems of the junipers so 

 common in the neighbourhood of Silverdale (near More- 

 cambe Bay) used to be distorted with Gymnosporangium, 

 and covered with the teleutospores of this fungus every 

 spring : in July all the hawthorn hedges in the neighbour- 

 hood had their leaves covered with the ^Ecidium form 

 {formerly called Rcestelia), and it was quite easy to show 

 that the fungus on the hawthorn leaves was produced by 



sowing the Gymnosporangium spores on them. Many 

 other well-established cases of similar hetercecism could 

 be quoted. 



But we must return to the Peridermium Pini. It wih 

 be remembered that I expressed myself somewhat 

 cautiously regarding the Peridermium on the leaves (var. 

 acicold). It appears that there is need for further inves- 

 tigations into the life-history of this form, for it has been 

 thought more than probable that it is not a mere variety 

 of the other, but a totally different species. 



Only so lately as 1883, however, Wolff succeeded in 

 infecting the leaves of Senecio with the spores of Perider- 

 mium Pini (acicold), and developing the Coleosporium, 

 thus showing that both the varieties belong to the same 

 fungus. 



It will be seen from the foregoing that in the study of 

 the biological relationships between any one plant which 

 we happen to value because it produces timber, and any 

 other which grows in the neighbourhood there may be 

 (and there usually is) a series of problems fraught with 

 interest so deep scientifically, and so important economic- 

 ally, that one would suppose no efforts would be spared to 

 investigate them : no doubt it will be seen as time 

 progresses that what occasionally looks like apathy with 

 regard to these matters is in reality only apparent 

 indifference due to want of information. 



Returning once more to the particular case in question, 

 it is obvious that our new knowledge points to the 

 desirability of keeping the seed-beds and nurseries 

 especially clean from groundsel and weeds of that 

 description : on the one hand, such weeds are noxious in 

 themselves, and on the other they harbour the Coleosporium 

 form of the fungus Peridermium under the best conditions 

 for infection. It may be added that it is known that the 

 fungus can go on being reproduced by the uredospores on 

 the groundsel-plants which live through the winter. 



H. Marshall Ward. 



(To be continued.) 



EARTHQUAKES AND HOW TO MEASURE 

 THEM. 1 



PROF. EWING explained that the study of earthquakes 

 had two aspects, one geological and the other 

 mechanical, and it was of the latter alone that his lecture 

 was to treat. The mechanical student of earthquakes 

 concerned himself with the character of the motion that 

 was experienced at any point on the earth's crust, and 

 with the means by which an earthquake spread from point 

 to point by elastic vibration of rock and soil. The first 

 problem in seismometry was to determine exactly how the 

 ground moved during an earthquake, to find the amount 

 and direction of every displacement, and the velocity and 

 rate of acceleration at every instant while the shaking 

 went on. He was to deal with the solution of that problem, 

 and to describe some of the results which had been 

 obtained in the measurement of earthquakes in Japan, 

 where earthquakes happened with a frequency sufficient 

 to satisfy the most enthusiastic seismologist. Most early 

 attempts to reduce the observing of earthquakes to an 

 exact science had failed because they were based on a 

 false notion of what earthquake motion was. It had been 

 supposed that an earthquake consisted of a single or at 

 least a prominent jerk, or a few jerks, easily distinguishable 

 from any minor oscillations that might occur at the same 

 time. The old column seismometer, for instance, recom- 

 mended in the Admiralty Manual of Scientific Inquiry, 

 attempted to measure what was called the intensity of 

 the shock by means of a number of circular columns of 

 various diameters which were set to stand upright like 

 ninepins on a level base. It was expected that the shock 



1 Abstract of a Lecture delivered at t^ie Royal Institution on Friday 

 evening, June i, by Prof. J. A. Ewing, K.R.S. 



