December 21, 1905] 



NA TURE 



171 



methods adopted were extremely simple. The tips of 

 growing roots, chiefly of seedlings, were injured in 

 various ways by making incisions into the region 

 about the apex, and the reactions that ensued were 

 carefully followed and compared. 



It was found, in confirmation and extension of the 

 less complete observations of Prantl and of Simon, 

 that the roots of ferns never truly regenerate them- 

 selves as do those of flowering plants. Possibly the 

 difference is to be attributed to the more definite con- 

 centration of formative protoplasm in the apical cell 

 of the former, as contrasted with its greater extension 

 as layers in the roots of the latter. At any rate, no 

 regeneration occurs in the roots of ferns, although 

 some attempts at healing the actual wound may be 

 made. 



The case is different with the roots of phanerogams, 

 although in them also the conditions of regeneration 

 are more limited than might have been anticipated. 

 In the first place, no union of the halves of longitu- 

 dinally cut roots took place ; the damaged apex was 

 either replaced by a new one on either side of the slit 

 or else the regeneration was confined to one half. 



An annular incision made just behind the tip of the 

 root into the cortex and extending as the endodermis 

 fails to give the stimulus requisite to produce a fresh 

 apex. Healing of the wound is more or less in 

 evidence, but the original apex continues to function, 

 and to supply cells for the further growth and elon- 

 gation of the root. But if the knife has passed 

 through the next layer, the pericycle, regenerative 

 phenomena at once set in. A new apex, with all the 

 complicated layers, is formed just behind (i.e. 

 proximally to) the wound, and it is especially interest- 

 ing to discover that the statolith starch now disappears 

 from the original tip, to be transferred to, or at any 

 rate to reappear in, the new one. 



Lateral incisions are ineffective to bring about the 

 differentiation of a new apex unless the slit has 

 severed at least half the circumference of the pericycle. 

 If this be done regeneration takes place, with the 

 concomitant appearance of statolith starch in the new 

 organ. All the experiments made on the roots go 

 to emphasise the great importance of the pericycle 

 in connection with regenerative processes, although 

 it is not from this layer itself that the new tip is 

 differentiated, but from the indifferent plerome cells 

 within it. The damage done to the pericycle appears 

 to act as an interruption of the coordinative relations 

 between the various parts of the embryonic region as 

 a whole. When this coordination is thus interrupted 

 the capacity of giving rise to entire organs that is resi- 

 dent in the embryonic protoplasm asserts itself, and 

 the new formation thus appears. We know as a 

 matter of fact that the pericycle retains the embryonic 

 condition until relatively late, since from it arise the 

 normally produced lateral roots. Of course, the pro- 

 cesses underlying the regenerative processes are by no 

 means cleared up by the experiments indicated above, 

 but at any rate certain definite facts have been ascer- 

 tained, and further lines of profitable investigation 

 readily suggest themselves. 



Comparatively few anomalous cellular effects were 

 NO. 1886, VOL. 73] 



observed. In the exceptional case of one fern root, 

 however, the nuclei of the healing (not regenerative) 

 cells exhibited irregularities both in their modes of 

 division and in the number of their chromosomes 

 which were commonly excessive. Multinucleate cells 

 were also observed in the plerome of a wounded root 

 of Ricinus, but they apparently took no part in the 

 actual regenerative processes. 



The book as a whole forms an important contribu- 

 tion to the literature of regeneration, its chief merit 

 perhaps lying in the numerous problems it suggests 

 for future investigation. It contains a bibliography 

 that should be useful, but it would have been materi- 

 ally improved by the addition of a good index. 



OUR BOOK SHELF. 

 Heredity. By C. W. Saleeby, M.D. Pp. n8, 



(London and Edinburgh : T. C. and E. C. Jack, 



n.d.) Price is. net. 

 The appearance of a little shilling book on 

 heredity is almost startling, when we consider the- 

 difficulty of the subject and the relative youth of its 

 exact study. That a book like this should be possible 

 indicates that considerable progress has been made 

 in recent years. Was it not Leibnitz who said, " The 

 more a science advances, the more it becomes con- 

 centrated in little books"? But it indicates also a 

 noteworthy skill on the author's part. Without 

 attempting to slur over difficult themes, e.g~ 

 Mendelism, as if they were easy, he has given us 

 a clear and interesting exposition, which will be 

 widely appreciated. It is a wonderful multum iv, 

 parvo, dealing lucidly, for instance, with the contrast 

 between hereditary resemblance and variation, be- 

 tween the germ-plasm and the body, between ger- 

 minal variations and somatic modifications, between 

 inherited nature and the results of nurture, between 

 inborn and congenital characters, and so on. Even 

 to have made these distinctions clear, so that thej 

 may be understanded of the people, is an achieve- 

 ment. As was natural in a book of this kind, the 

 author takes up an eclectic position, and quotes freely 

 from various writers — from one about ten times. He 

 is inclined to allow that there is a limited trans- 

 mission of " acquirements " or modifications, but the 

 only instance we have found is an inept one — that 

 bacteria may transmit an exaltation of their virulence. 

 He agrees with Dr. Archdall Reid on many points, 

 e.g. that amphimixis never produces more than re- 

 gressive variations, but does not think that this 

 author satisfactorily accounts for the origin of spon- 

 taneous variations. He has the same complaint to. 

 make of Weismann, but in regard to a view which 

 that progressive biologist no longer holds, as, indeed, 

 the author seems to know (p. 54). We may also note- 

 that even in " The Germ-Plasm " Weismann did not 

 teach that " parthenogenetic species cannot vary " ;- 

 in fact, he made experiments showing reversion in 

 parthenogenetic generations of Cypris. There is a 

 useful chapter on " physical degeneration," but we 

 do not understand the author when he says that those 

 who believe in progressive degeneration " have it 

 incumbent upon them to demonstrate either the falsity 

 or the suspension of the law of natural selection." 

 Surely the many " degenerate " animals that we 

 know have not become what they are without the 

 help of selection. Another point that we do not 

 understand is how the fact that " one-half of tin- 

 nuclear chromatin of each gamete is thrown aside 

 prior to the fusion of the two nuclei," " obviously 



