June I, 1888.] 



SCIENTIFIC NEAVS. 



517 



Hypocrisy of a Dog. — Prof. S. V. Clevenger 

 (American Naturalist) mentions that a dog which had 

 had a severe cold and cough was allowed to stay in the 

 house. Since his recovery if any mention is made of 

 turning him out of doors he coughs vigorously, and 

 wheezes in fair imitation of asthma. When turned out 

 he at once drops the pretence and rushes oft' in search 

 of company. 



Evolution v. Special Origination. — It is now found 

 that the doctrine of the fixity of animal and vegetable 

 species is due mainly to John Milton and John Ray. It 

 W3S rejected by Bacon and by St. Thomas Aquinas. 



A Colour- yielding " Germ." — M. Galtier 

 Rcndits) has observed a morbid bacillus which, if placed 

 in contact with various kinds of organic matter, such as 

 gelatine, beef-broth, or potato, has the power of generat- 

 ing a peculiar green colour, inclining in some cases to a 

 yellow and in others to a bronze. This discovery sug- 

 gests some interesting possibilities. Shall we some day 

 employ bacilli, or other microbia, in manufacturing 

 colours for the dyer, and perhaps producing them on the 

 tissues themselves ? 



— ■•-^»^«^*tf-» — - 



RELATIONS OF ANIMALS TO PLANTS. 



BETWEEN the animal and the vegetable world there 

 prevails for the most part a state of hostility. 

 From man, who in his mistaken greed cuts down every 

 tree in his neighbourhood, to the goat which browses 

 away young saplings, the hare and rabbit which gnaw- 

 away the bark, the phylloxera which ravages vineyards, 

 the cockchafer, the caterpillar, and the locust which 

 consume leaves, not to speak of myriads of other species, 

 we perceive a constant war being waged against plants. 

 It is therefore consolatory to find some instances of an 

 opposite kind. To what an extent bees, butterflies, and 

 even one family of two-winged flies, the Syrphidm, are 

 instrumental in effecting the fertilisation of flowers is 

 now very generally known. But other instances are 

 coming to light. Thus it has lately been shown that 

 even certain ants — those, at least, which do not cut 

 leaves and domesticate aphides — may be of service to 

 plants. Thus our regretted friend, Thomas Belt, men- 

 tions, in his charming " Naturalist in Nicaragua," that a 

 kind of acacia, the buU's-horn thorn, keeps an army of 

 venomous ants (Pscitdomyrma bicoloi-), which protect it 

 both from browsing mammalia, from caterpillars, and 

 from leaf-cutters. These guards receive as their pay a 

 honey-like liquid, secreted at the base of each pair of 

 leaflets, and on a little j'ellow, fruit-like body at the end 

 of each of the small divisions of the compound leaflet. 



Some interesting researches of Axel Lundstrom 

 ( Transactions of the Royal Society of Upsala, abstracted in 

 Humboldt) show that even certain mites are found 

 associated with plants in a manner mutually beneficial. 

 Here great caution is needed, since the so-called " red 

 spider," justly dreaded in vineries, is a member of the 

 same order. We must therefore regret that Dr. 

 Lundstrom, or his abstractor in Humboldt, has not given 

 us the names of the species which he has studied. We 

 suspect that they must belong to the families of 

 Trombididce or Canasydce. 



A mite, it must be remembered, though a tiny 

 creature is by no means an insect, but is much more 



nearly related to the Crustacea (crabs, shrimps, etc.) 

 and to the Arachnida (spiders, scorpions, and the like). 



Lundstrom has noticed that on the underside of the 

 leaves of the lime, alder, elm, hazel, and plane there are 

 found at the junctions of the nervures little tufts of hairs. 

 These form dwellings in which the Ught-dreading mites 

 spend the day. Here they are born, grow up, and die. 

 An anatomical examination of the leaves shows that in 

 these hiding-places both the epidermis and the under- , 

 lying assimilative tissue differ plainly from other parts 

 of the leaf Not merely the form, but the contents of 

 the cells seem here peculiar. These facts place it 

 beyond doubt that we have here a mutual relation 

 between the leaf and the mite ; in short, a phenomenon 

 of adaptation. Turning to other plants, Lundstrom 

 found in them also identical or, at least, analogous 

 relations. Thus, in Lonicera xylosteum and L. alpigena, 

 the mites occupy minute, peculiarly-shaped pits or 

 pockets on the lower surface of the leaves ; in the ash 

 [Fraxinus excelsior), they dwell in a groove in the rachis ; 

 in the gooseberry and in Ribes alpinum we find colonies 

 of mites in pocket-like structures at the base of the 

 lower side of the leaf Among tropical plants, especially 

 in the Rubiacece, cases of such association with mites were 

 much more frequent. 



Lundstrom then inquired whether these peculiar 

 arrangements pre-existed in the plant";, or whether they 

 were subsequentlj' occasioned by the mites, and further, 

 what advantage, if any, the plants could derive from this 

 living in common (symbiosis). He therefore raised 

 plants from seed in such a manner as to be absolutely 

 free from mites. To his surprise many of the seeds did 

 not germinate. When he finally succeeded in getting 

 young plants perfectly without mites, he still found 

 the peculiar structures — pits, pockets, folds, tufts, etc. — 

 whence he infers that they are not of a morbid character. 

 Still, he observed that if the plant is kept for a consider- 

 able time perfectly free from mites, these habitations do not 

 become perfectly developed, and are even reduced in 

 number. Hence Lundstrom conjectures that they were 

 originally occasioned by the action of the mites, being 

 consequently of pathological nature, but have since 

 become hereditary. 



To determine the importance of the mites for plants 

 it was necessary to inquire into their functions. Lund- 

 strom finds merely that they eat, excrete, and breathe, 

 giving off carbonic acid. If it be asked. What is their 

 food ? he finds that it is not the juices of the plant, but 

 the spores and hyphae of fungi. Hence they protect 

 the plants which they inhabit against the attacks of 

 parasitic fungi — surely a service of no trifling impor- 

 tance. 



They are useful to plants, further, by their nitrogenous 

 excretions, and by the carbonic acid which they exhale. 

 For, as it has been already remarked, the assimilative 

 tissue lying immediately under the habitations of the 

 mites is often different, both in form and contents, from 

 similar tissue in other portions of the leaf. But further, 

 Lundstrom has succeeded in proving directlj" that the 

 excrements of the mites gradually vanish down to a thin 

 film. It seems to him not improbable that the subjacent 

 cells secrete an agent which dissolves the excrements 

 and renders them capable of absorption and assimilation 

 by the cells. This would seem to show that the carni- 

 vorous plants are not alone in being able to utilise 

 complex organic food without its previous decomposition 

 into ammonia or oxides of nitrogen. 



