Jan. 5, 1888] 



NATURE 



227 



sis ^ is known to arise as a paired epiblastic involution 

 (Dohrn). In the Cyclostomata it is formed as an epi- 

 blastic involution (possibly paired) at the extreme anterior 

 end of the body. In one Vertebrate alone, Alyxine {vide 

 figure), it still opens into the hypoblast ; in all others it 

 approaches the hypoblast in development, but does not 

 fuse with that layer. It always lies in very close relation- 

 ship with the extreme end of the notochord — that is, with 

 the end of a structure derived from the hypoblast. 



In adult Petromyzon, in which the tube of the oral 

 hypophysis has the same relationships as in Myxine, ex- 

 cept that the posterior opening into the hypoblastic sac 

 is absent, it nevertheless has an astonishing length, 

 and ends blindly very close to the gut. In Myxine and 

 Petromyzon, tubular glands are developed in connection 

 with it. In all the higher Vertebrates, in which the oral 

 part is very rudimentary, it always has a distinct glandular 

 character. 



And now, what of the last condition? This also is 

 satisfactorily met. In all cases the oral hypophysis has a 

 special, and indeed large, process of nervous matter (the 

 processus infundibuli, or neural hypophysis), which is 

 derived from the posterior part of the fore-brain, from the 

 base of the infundibulum. This process is concerned 

 with the innervation of the oral hypophysis alone. In 

 Myxine and Petromyzon alone, so far as my researches 

 €xtend (possibly also in Protopterus), this nervous system 

 is not rudimentary. In most Vertebrates the neural 

 hypophysis, which, as KoUiker aptly remarks, is at first 

 composed of the same cell elements and fibres as the rest 

 of the brain, degenerates, and in very many full-grown 

 animals forms a mass of tissue, the structure of which 

 many observers have compared to that of the suprarenal 

 bodies (known to be masses of degenerated tissue). 



The neural hypophysis is thus the most remarkable 

 structure in the whole of the Vertebrate central nervous 

 system. Though degenerated, it still clings to the tradi- 

 tions of its ancestry, for even, as it were, in its death it is 

 closely and almost inseparably connected with the rest of 

 the hypophysis, especially in Mammalia and in Dipnoi. 

 In Myxine alone, of all Vertebrates, the old mouth still 

 retains some of its functions as a mouth ; it conducts the 

 water of respiration to the gills. In this case, even, 

 changes have occurred, for the nose - (see figure, n.f.) 

 has got partly involved in the passage of the old mouth. 

 If it be true that the nose was originally a branchial 

 sense-organ — which view, in spite of Gegenbaur, I still 

 maintain — its assumption of a position in the passage of 

 the old mouth in Myxine is, on purely physiological 

 grounds, intelligible. 



It is well known that that which I call the old mouth 

 in Myxine is purely respiratory, conducting water into 

 the gills ; and what then could be more likely than that 

 one of the branchial sense-organs should be, as it were, 

 told off to do duty at its entrance. It is certain, from 

 Goette's and Dohrn's researches, that these passages in 

 Myxine and Petromyzon are the representatives of the 

 oral hypophysis. I have gone over and extended these 

 observations, and can fully confirm Dohrn in nearly every 

 point, and all I claim here is the identification of the 

 hypoplastic opening in Myxine as the (modified) opening 

 of the old mouth into the gut. 



If the above morphological comparison can be main- 

 tained (and I believe it can), the importance of its 

 bearing on the morphology of Vertebrates can hardly be 

 over-estimated. 



A number of other problems and conclusions arise out 

 of all this, but I reserve the consideration of these for a 

 much more exhaustive work, in which the literature of 

 the subject will receive full attention. J. Beard. 



Anatomisches Institut, Freiburg i/B., November 16. 



' I believe it is very frequently paired, though not at its point of origin. 

 In Petromj'zon, Uohm finds that the nose is at first a special depression 

 apart from the hypophysis invaginatioa. The larter lies between the nose 

 and mouth. 



TIMBER, AND SOME OF ITS DISEASES?- 



III. 



TTAVING now obtained some idea of the principal 

 *• -*■ points in the structure and varieties of normal 

 healthy timber, we may pass to the consideration of some 

 of the diseases which affect it. The subject seems to 

 fall very naturally into two convenient divisions, if we 

 agree to treat of (i) those diseases which make their 

 appearance in the living trees, and (2) those which are 

 only found to affect dead timber after it is felled artd 

 sawn up. In reahty, however, this mode of dividing the 

 subject is purely arbitrary, and the two categories of 

 diseases are linked together by all possible gradations. 



Confining our attention for the present to the diseases 

 of standing timber — i.e. which affect undoubtedly living' 

 trees — it can soon be shown that they are very numerous 

 and varied in kind ; hence it will be necessary to make 

 some choice of what can best be described in this article. 

 I shall therefore propose for the present to leave out of 

 account those diseases which do injury to timber in- 

 directly, such as leaf-diseases, the diseases of buds, 

 growing roots, and so forth, as well as those which do 

 harm in anticipation by injuring or destroying seedlings 

 and young plants. The present article will thus be 

 devoted to some of the diseases which attack the timber 

 in the trees which are still standing ; and as those caused 

 by fungus parasites are the most interesting, we will 

 for the present confine our attention to them. 



It has long been known to planters and foresters that 

 trees become rotten at the core, and even hollow, at all 

 ages and in all kinds of situations, and that in many cases 

 the first obvious signs that anything is the matter with 

 the timber make their appearance when, after a high 

 gale, a large limb snaps off, and the wood is found to be 

 decayed internally. Now it is by no means implied that 

 this rotting at the core — " wet-rot," " red-rot," &c., are 

 other names generally applied to what is really a class of 

 diseases — is always referable to a single cause ; but it is 

 certain that in a large number of cases it is due to the 

 ravages of fungus parasites. The chief reason for popular 

 misconceptions regarding these points is want of accurate 

 knowledge of the structure and functions of wood on the 

 one hand, and of the nature and biology of fungi on the 

 other. The words disease, parasitism, decomposition, 

 &c., convey very little meaning unless the student has 

 had opportunities of obtaining some such knowledge of 

 the biology of plants as can only be got in a modern 

 laboratory : under this disadvantage the reader may not 

 always grasp the full significance of what follows, but it 

 will be at least clear that such fungi demand attention as 

 serious enemies of our timber. 



It will be advantageous to join the remarks I have to 

 make to a part description of some of the contents of 

 what is perhaps one of the most instructive and remark- 

 able museums in the world — the Museum of Forest Botany 

 in Miinich, which I have lately had the good fortune to 

 examine under the guidance of Prof. Robert Hartig, the 

 distinguished botanist to whose energy the Museum is due, 

 and to whose brilliant investigations we owe nearly all that 

 has been discovered of the diseases of trees caused by the 

 Hymenomycetes. Not only is Prof Hartig's collection 

 unique in itself, but the objects are classical, and illus- 

 trate facts which are as yet hardly known outside the 

 small circle of specialists who have devoted themselves 

 to such studies as are here referred to.' 



One of the most disastrous of the fungi which attack 

 living trees is Trametes radiciperda (Hartig), the Polyporus 

 annosus of Fries, and it is especially destructive to the 

 Coniferae. Almost everyone is familiar with some of our 

 common Polyporei, especially those the fructifications of 

 which project like irregular brackets of various colours 

 from dead stumps, or from the stems of moribund trees ; 



' Cor.tin ;e I from p. 207. 



