' planters in this country. 
APRIL 25, 1912] 
LETTERS TO THE EDITOR. 
{The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
Insect Parasites on Trees. 
Tue note in Nature of April 11 (p. 144) about the 
ravages of insect parasites upon the chir pine (Pinus 
longifolia) in the Himalayas suggests a consideration 
which, I think, is not enough present to foresters and 
1 am too destitute of 
biological or physiological knowledge to venture an 
opinion upon the causes. which lead to the excessive 
multiplication of parasites, whether animal or fun- 
goid, upon animals and plants whereof the vitality 
has been impaired by some other agency; but the 
phenomenon must be familiar to most people, though 
it is generally wrongly interpreted. Normally 
vigorous organisms may, and do, entertain a reason- 
able number of parasitic guests without appreciable 
loss of vigour; but these guests seem to bide their 
time until the host is weakened by accident or 
disease, when they display a surprising amount of 
latent fecundity. In the case of the chir pine, the 
opportunity occurs when the vitality of the tree is 
lowered by tapping for resin; in other words, when 
it is depleted of its protective juices, the diminution 
of which gives easy access to the Platypus larve. 
To an analogous process may be traced the preva- 
lence of larch canker, which, during the last fifty 
years, has brought such heavy loss upon owners of 
woodland, having previously attracted no attention 
whatever from foresters. It has now become the 
most widely destructive tree disease in Britain. The 
hostile agent in this case is a pesizoid fungus, 
Dasycypha calycina, the ravages of which generally 
manifest themselves on poles from seven to fifteen 
years old. Many of these die or become hopelessly 
deformed, and all attempts to arrest the evil have 
hitherto proved futile, although recent works on 
forestry bristle with recommendations on the subject. 
Yet I am convinced that planters have the remedy in 
their own hands—at least as regards planting in the 
future. 
The fungus Dasycypha is no new creation; it has 
always found a home on the larch. Dr. Hartig found 
traces of it in Swiss larch of 100 years’ standing. I 
have found it also on Corsican and Scots pines, where 
it is quite innocuous. The European larch has suc- 
cumbed to its attack in Great Britain because, under 
the conditions to which foresters too often expose 
them, the young plants receive a severe check at the 
critical time of planting, and do not recover strength 
before the mycelium has penetrated the tissues so far 
as to hinder or prevent recovery. 
This check is the result of the drying of the roots 
during transport from a distant nursery. There is 
Dasycypha in the noble larch woods of Dunkeld, but 
no cankered larches. The parasite has never had a 
chance of overcoming its host, because these trees 
were all reared from seed in home nurseries and 
planted out straight away. 
The Japanese larch (Larix leptolepis) is very nearly 
akin to the European species, but is distinguished 
by its immensely superior vigour in youth. Hence, 
although the characteristic larch parasites—Dasy- 
cypha, Chermes, and the large larch sawfly—may all 
be found in a plantation of Japanese larch here, the 
trees are none the worse for their presence. 
The lesson to be learnt by our foresters seems to 
be that although the native climate of the European 
NO. 2217, VOL. 89] 
NATURE 
Ig! 
larch is very different from that of the British Isles, 
it adapts itself readily to British conditions, provided 
that care be taken to protect it from any check to 
its vitality, and that they may treat with indifference 
prescriptions against this and other tree diseases for 
exterminating parasites or checking their attacks, 
such as hand-picking, smoking, spraying, &c., all 
of which are childish in their futility and prohibitive 
in expense when applied to large woodland areas. 
Monreith, April 15. Herbert Maxwe er. 
The Propagation of Long Electric Waves during the 
Solar Eclipse. 
Ir is now common knowledge that the long electric 
waves employed in wireless telegraphy over great dis- 
tances appear to travel better during the hours of 
darkness than in the daytime. It is known besides 
that the natural electric waves produced by atmo- 
spheric electrical discharges—which are heard in the 
telephones of receiving stations as clicks or scratching 
noises, and are called ‘‘strays” or “X’s” by those 
engaged in wireless telegraphy—are also propagated 
better in darkness than in light. 
These differences between day and night propaga- 
tion suggested to me that observations of the strength 
and number of strays, and of the strength of signals, 
during the solar eclipse of April 17, might prove 
to be of interest. Accordingly a record of strays and 
signals was made at my laboratory in London during 
the progress of the eclipse. The apparatus was set 
so as to receive signals of wave-length 5500 metres, 
which is approximately the wave-length of the signals 
emitted from the Marconi Transatlantic station in 
Ireland. 
About the time of the eclipse strays were fairly 
numerous. The table below is a convenient summary 
of them. The number entered under each of the 
times was obtained by making a sort of rough time- 
integral of the number and intensity of the strays 
heard from half a minute before to half a minute 
after the beginning of the minute indicated. 
Time 11.46am. 47 48 49 5O 51 52 53) end 55 
Strays 1c 10 Iz 12 13 17 21 20 21 22 
Time x1.56am. 57 58 59 m2’0mnoon x 2 3 4 5 6 7 8 
Strays 22 17) 12) x2 13 <5 149) 18) x2 24) agi 23 
‘Time! 12.9) mo) irr sae: Wes” ivaa ine) 6) arg 5 8) 19. 20) 26 
Strays 25 24) 26 i777 e422 eer) 90.) ao) 27, 14 
Time 12:22 23 24 25 26 27 28 29 30 3r 22 33 34 
Strays 13 PRs eres yids Mv pene ine!) 3s 
ov. 
y 
Time 1236 37-38 39, go, g2 ge G7 
Strays 12 11 Ir 10 10 10 12 14 14 14 12 10 
These results are exhibited in the curve, with the 
times as abscissze. 
_~. 
’ 
‘ 
ae 
aN 
a0 sO /2n00n 10 20 30 40 50 
The message-bearing waves from Clifden were 
brief and irregular, so no measurements of their 
intensity were obtained; but it was very noticeable 
that they were loud when the strays were loud, and 
vice versa. 
The observations show that on the whole the dark- 
