414 



NATURE 



[June 2, 1910 



Great Oolite beds, possibly some Lower Greensand, and 

 in every boring Gault and Upper Greensand. The 

 omissions in the series are notable ; we have no certain 

 Carboniferous rocks, only a possibility of Trias, no Lias, 

 only one division of the great Jurassic series, and no 

 Wealden beds, a perfect succession being reached only with 

 the Gault, 



To the description of the Chalk nine pages are given, 

 and as the Middle and Lower divisions are found only 

 underground, in borings, these are concerned chiefly with 

 the Upper Chalk. The zones of the whole formation, with 

 the distinctive fossils, are noted. 



The Eocene Tertiaries, which form so large a part of 

 the district, take twenty-five pages for their description, 

 which are followed by four pages on faults and disturb- 

 ances, after which the various members of the great Drift 

 series, so greatly in evidence in the district, are described 

 at some length, the Older Drifts with eleven pages to 

 their credit, the Glacial (and allied) Drift with thirteen, 

 whilst the description of the Valley Drifts, with their flint 

 implements, extends to twenty-three pages. 



The stratigraphic series ends with Recent beds, the 

 Alluvium of the rivers being described in eight pages, after 

 which the remaining ten pages of the chapter treat of 

 some other matters, namely, a description of the Thames, 

 its tributaries and its buried rivers, floods, fords, old 

 trackways, a short account of the growth of London, and 

 a summary of the physical changes in the district from 

 the time of the deposit of the Chalk to the formation of 

 the Alluvium. 



The question of water-supply from the various beds is 

 discussed in nine pages, and various other economic 

 questions in other ten, which conclude the work, except 

 for the lengthy index. 



The plate is a contour-map of the district, with a 

 geologic section from the valley of the Gade, on the north- 

 west, to beyond that of the Darent, on the south-east. 



At the end of the various subjects a list of the chief 

 works relating to each is given, and this will be of much 

 use to those who want further detail. But with this 

 memoir in hand nearly everyone may know as much about 

 the geology of London, using that name in a wide sense, as 

 he needs to know. 



ECONOMIC ENTOMOLOGY. 



I 



N the last number of the Journal of Economic Biology 

 (vol. v., pp. 9-17) Mr. W. E. CoUinge gives some 

 interesting notes on the form of the egg of the horse bot- 

 fly (Gastrophilus equi), its attachment to the horse's hair, 

 and the method of its hatching. The narrow end of the 

 subconical egg is not simply glued to the hair ; it clasps 

 the hair by means of a pair of ridges or lips, so that the 

 area of attachment is like that of the ox warble-fly (Hypo- 

 derma bovis), only less specialised. With regard to the 

 mode of hatching, Mr. Collinge's observations and experi- 

 ments confirm, in the main, the statements of Bracy Clark 

 and Osborn. He found that the eggs were most readily 

 induced to hatch, by the application of moisture, from 

 sixteen to twenty days after hatching; none could be 

 induced to hatch after thirty-six days. 



. Mr. R. Newstead describes in the same part (pp. 18-22) 

 a couple of new species of Coccidae from the Congo, which 

 live as guests of ants (Cremastogaster and Sima) in their 

 nests in the hollow shoots of plants. It is very rarely that 

 insects of this family are found in the hollow stems of 

 their food-plants. One specimen contained a minute 

 lepidopterous larva which had partly destroyed its host. 



It is welLJ<nown that economic entomologists in North 

 America are much troubled by the ravages of insects pur- 

 posely or accidentally imported into their country from 

 Europe ; one of the mdst famous of these is the gipsy moth 

 (Porthetria dispar). Dr. L. O. Howard has lately (U.S. 

 Dept. Agric. Bur. Entom., Tech. Ser., 19) described some 

 parasites reared from the eggs of this insect. It is remark- 

 able that the parasites- — various species of minute Hymeno- 

 ptera — all come from Hungary, Russia, and Japan. From 

 Gipsy-moth eggs imported from western Europe no parasites 

 could be reared, and, though the moth has been in the 



NO. 2 I 18, VOL. 83] 



United States for more than forty years, no American 

 species is known to attack its eggs. " Non-parasitism of 

 F. dispar by native species," writes Dr. Howard, " is 

 probably due to the character of its egg-mass, which is 

 so compact and so thoroughly protected by the scales of 

 its parent as possibly to disguise its character from species 

 unacquainted with it." G. H. C 



'^1 



ALTERATIONS OF THE DEVELOPMENT AN. 

 FORMS OF PLANTS AS A RESULT OF 

 EN VJRONMENT} 

 'T'HE fungus Saprolegnia is chosen as an example among 

 the lower plants. This fungus lives on dead insects, 

 and shows three distinct stages of its development :— 

 (i) vegetative growth of the mycelium ; (2) asexual repro- 

 duction by motile zoospores ; (3) sexual reproduction by 

 male and female organs. Under ordinary conditions these 

 three stages follow one another quite regularly until, after 

 the ripening of the resting spores, the fungus dies ; but, 

 according to the special conditions of every stage, it is 

 possible to produce them as we desire, and also to alter 

 their succession. Under very favourable conditions of 

 nutrition the fungus must continuously grow, without being 

 propagating and without dying. Numerous other lower 

 plants, as fungi and algae, show the same relations to 

 environment. 



Flowering plants present far more diiliculties, in con- 

 sequence of their very complicated structure. Semper- 

 vivum Funckii is taken to show how far the development 

 of such a plant depends on environment. Sempervivum 

 appears as a short stem covered with thick sappy leaves ; 

 we call this form a rosette. The rosettes produce in an 

 asexual way new daughter-rosettes, of which each comes 

 to flower under suitable conditions, and dies after the 

 ripening of seeds. The state of a plant, destined to flower 

 but without recognisable rudiments, is called ripe to power. 

 The formation of the inflorescence consists of three essentia: 

 stages : — (i) the lengthening of the stem ; (2) the produc 

 tion of several branches at the top ; (3) the birth ol 

 flowers. 



Under very favourable conditions of nutrition, a rosett4 

 ripe to flower can be transformed again into a vegetativ« 

 one, which must always grow without sexual reproduction, 

 In blue light, during March and April, a lengthening of th« 

 rosette ripe to flower takes place, but without flowering 

 Such a lengthening of the stem is wholly independent o 

 flowering, because all rosettes, also the youngest ones, arj 

 able to lengthen in red light. On the other hand, the flowen 

 can result without lengthening when the rosettes are ex 

 posed to a high temperature. The production of flowerinj 

 branches can be prevented, the inflorescence at the en< 

 having but a single flower. In other conditions numeroui 

 branches are to be found on the whole stem, even in _th( 

 axils of the old leaves, particularly as the result of injuries 



We come to a new series of forms by replacing flower 

 by leaf-rosettes, which can be produced on all parts of th( 

 inflorescence, even on the flowering branches, alone o; 

 mingled with flowers. The plants, of which the in 

 florescence bears rosettes, do not die at the end of summe 

 as is normal, but live another two or more years, appear 

 ing in peculiar forms. It can be shown that flowers var 

 in an exceedingly high degree under certain conditions 

 The number and arrangement of all members as sepals 

 petals, stamens, and carpels can be altered. Furthe 

 striking variations of the normal forms appear in sucl 

 artificially modified flowers by the transformation of sepal 

 into petals, of petals into stamens, of stamens into petal 

 and into carpels. Experiments were made to answer th( 

 question whether alterations of flowers can be transmitted 

 For such researches Sempervivum acuminatum, which pro 

 duces easilv ripe seeds, was used. The seeds of flowen 

 artificially 'altered and self-fertilised gave rise to twenty 

 one seedlings, among which four showed surprising devi^ 

 tions in their flowers. With two seedlings all the flo\yer 

 were greatly altered, and presented some of the alteration! 

 of the mother plant, especially the transformation or 

 stamens into petals. The experiments are being continued. 



1 Abstract of the Ooontan Lecture delivered at the Royal Society on 

 May 26 by Prof. G. Klebs. 



