November 17, 189S] 



NA TURE 



69 



uniform ; and its basal position is also uniform, though some 

 difference of detail does appear in the relation of this absorbing 

 body to the first segmentation of the embryo. 



In the Pteridophyta it is exceedingly difficult to be sure of the 

 correspondence by descent of the foot in distinct types, and 

 indeed it should not be assumed that a specialised absorbent 

 orqan was always present, though general surface-absorption 

 will naturally have taken place in all archegoniate embryos ; 

 indeed the condition of some upright embryos is such that a foot 

 would never have been described, were it not for comparison 

 with other types. In Ei/uise/iini, /socles, Botrychiiiin — all 

 forms without a suspensor, and with an upright growing embryo 

 — the hypobasal half of the embryo, with or without a root, is 

 absorbent as in the Bryophyta, and is described as a foot ; it is 

 quite possible to see in them the continuation of a primitive 

 absorbent organ. This may also be the case in the Marattiaceae, 

 and it is specially noted by Campbell that " in Maraltia all the 

 superficial cells of the central region become enlarged and act 

 as absorbent cells for the nourishment of the embryo." From 

 such types we may imagine the more specialised foot of the 

 Leptosporangiate Ferns to have been derived by a localisation 

 of the absorbent function on one side only, which would be a 

 natural consequence of the embryo taking the prone, in place of 

 the vertical position. 



A different course of events probably occurred in the 

 Lycopodinece. I am disposed to think that here the suspensor 

 represents nothing more than a specialised part of the primitive 

 absorbent organ ; this seems to be indicated by the details as 

 shown in Treub's figures of L. icniiiuin and Z. Phlcgiimria, in 

 which the suspensor is continuous with the foot. But what is 

 then the "foot" of Selap'iiel/a, which is quite apart from the 

 suspensor, the root intervening? On this point I think we 

 obtain light from Welwitschia and Gnetuin, for in these we see 

 an absorptive organ formed at a comparatively late period ; and 

 it corresponds in position and function, though not in time of 

 origin or details of structure, with that of Selaginel/a. I con- 

 clude that the " foot '' of Sclaginella is probably a later form- 

 ation, not comparable as regards descent either with the foot of 

 Lyiofodiiim , or with the " feeder" of Welwitschia or Gnetum. 

 The latter are plainly of recent independent origin, as compari- 

 son shows, and their actual position is defined according to the 

 position of the seed in germination. Probably, then, there is 

 homoplasy in such cases, not true homogeny. 



Similarly with such structures as the pinnae, stipules, in- 

 dusium, corona, and still more so with such inconstant bodies 

 as emergences and hairs ; when we speak of the " homologies " 

 of these parts it is rarely the homogeny, or identity by descent, 

 which we mean to express ; usually it is only homoplasy, a 

 comparison of parts similar, it may be, in form and position, or 

 even in development and function, though not shown to be 

 comparable by descent. 



Alternation. 

 But the questions above discussed are mere matters of detail, 

 compared with that great enigma of the alternation of genera- 

 tions in green plants, or of alternation at large. This is, after 

 all, a question of degree of homology, not now of the parts 

 only, but of the whole plant or "generation." How this 

 greatest of all adaptations was really initiated, we cannot expect 

 to bring to the point of demonstration ; at best we can only 

 venture opinions of probability. Still this discussion com- 

 mands at present more widespread interest among botanists 

 than any other in the sphere of plant morphology. 



There was a time when the attempt was made to reduce all 

 plants to one scheme as regards their life-cycle, a method which 

 not only prevented elasticity of theory, but was responsible for 

 some unfortunate comparisons. It was characteristic of the 

 period when the text-book of Sachs reigned supreme ; we find 

 it there definitely laid down that " the doctrine of alternation 

 has the object of reducing to one scheme the main phases of 

 the life of all plants which bear sexual organs." But the con- 

 troversy between Pringsheim and Celakovsky had, as one of its 

 results, the recognition of various types of life-history, not of 

 one scheme only. The tendency at present is towards the 

 opposite extreme ; the frequency of the parallel developments 

 now recognised has led some to accept a comprehensive poly- 

 phyletic view as regards alternation, and wherever difficulties of 

 comparison arise, to take refuge in the plausible suggestion that 

 the organisms compared represent altogether distinct lines of 

 descent. But the view which should be confidently upheld, is 

 that even where this may actually be the case useful comparisons 



NO. I 5 16, VOL. 59] 



may yet be made : and that the method of progress within one 

 phylum may illustrate the probable mode of progress in another. 

 The green Alga; may thus throw light upon the probable origin 

 of the sporogonium in the Bryophytes, though they may in no 

 sense be in the line of their descent ; the Bryophytes may 

 suggest valuable ideas for the comparative study of the 

 Pteridophytes, though they may not represent their actual 

 ancestry. 



It is the alternation as seen in these green plants that I pro- 

 pose to discuss. Writers have distinguished various types of 

 alternation, including under the term divers modes of " alter- 

 nation of shoots " ; and it should be remembered that this was 

 the original sense of the word alternation as applied by Steen- 

 .strup. But gradually the issue in the case of green plants has 

 been simplified, and the question now centres round that 

 alternation of phases which some of us describe as "antithetic," 

 while others believe the phases to be really "homologous" a.s 

 regards their origin. 



Briefly put, the question is, How was the first start inade ? 

 Has the neutral generation or sporophyte been the result of 

 change of any other part of the sexual generation than the 

 zygote itself? If so, the alternation is of homologous generations ;. 

 if not, then the alternation is what is styled antithclic. The 

 whole discussion is like a purely historical inquiry, but with 

 the minimum of documentary evidence ; for on this point the 

 fossils give scanty help. In the absence of more direct evidence 

 we are thrown back on other aguments, such as those based oa 

 comparison of normnl specimens, and secondly upon the study 

 of abnormalities. I shall not attempt to treat the matter ex- 

 haustively ; it will, however, be necessary for me to deal with 

 certain points in the discussion which were raised in the able 

 address of Prof. Scott at Liverpool. He there restated Prings- 

 heim's view of homologous alternation as against the antithetic. 

 I propose now to consider three matters which I think are most 

 material to the discussion, viz. (i) the bearing of the Algae and 

 certain Fungi on the question ; (2) the comparison from the 

 Bryophyta ; and (3) the argument from abnormalities. 

 ( To he continued. ) 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge. — At the conjoint examination for entrance 

 scholarships, just completed, the following awards have been 

 made in Natural Science. At Pembroke College : Scholar- 

 ship, G. H. Delf, Camberwell Grammar School, 40/. At 

 Gonville and Caius College : Exhibition, M. M. L. Rittenberg, 

 Tonbridge School, 30/. At Jesus College : Scholarship, J. 

 Hewitt, Derby School, 40/. At Christ's College : Scholarship, 

 C. H. B. Epps, City of London School, 40/. : exhibition, R. B. 

 S. Sewell, Weymouth College, 30/. At St. John's College : 

 Scholarship, G. C. E. Simpson, Mill Hill School, 60/. ; Lupton 

 and Hebblethwaite Exhibition (open /TO liac vice), J. F. Hough, 

 Mason University College, Birmingham ; Johnson Exhibition 

 (of<tx\ pro hac vice), B. E. Mitchell, Brighton Grammar School. 

 At Emmanuel College : Scholarship, H. U. B. Banham, Ipswich 

 Grammar School, 40/. ; exhibition, A. C. H. Rothera, Market 

 Bosworth School, 30/. Clare College : Scholarships of 60/. to 

 E. B. Bailey, Kendal Grammar School, and W. Cartwright, 

 Middlesburgh Grammar School. Trinity College : Minor 

 Scholarship of 75/. to C. S. Coles, University College, London ; 

 Exhibitions of 40/. to J. Frame, Mason College, Birmingham ; 

 C. W. Hutt, St. Paul's School, London ; T. C. James, 

 Aberystwyth University College ; H. Lambert, Perse School, 

 Cambridge. 



Mr. F. G. Hopkins has been appointed University Lecturer 

 in Chemical Physiology. 



The degree of LL.D. will be conferred on Lord Kitchener 

 of Khartoum on November 24. 



The Clerk Maxwell Studentship in Experimental Physics 

 will be vacant at the end of this term. Candidates, who must 

 have worked in the Cavendish Laboratory, are to send their 

 names to Prof. Thomson by December 9. 



It is proposed that Advanced Students shall be admitted to 

 Part II. of the Mechanical Sciences Tripos, and that for the 

 B. .\. degree they shall be required to attain the standard of the 

 Second Class at least. 



The General Board of Studies have proposed a scheme for 

 the establishment of an Allen Research Studentship under the 



