432 



NA rURE 



[August 23, 1906 



be ascertained, such have not been forthcoming, nor can 

 I hear of any record of recent Mangroves being preserved 

 in this way. Seeds and embryos appear to be so uniform 

 on the whole that it is difficult to understand how they 

 could have passed through a viviparous phase in the later 

 stages of their evolution. 



The viviparous Mangroves, on the other hand, are full 

 of diversity in detail, and these differences would surely 

 have left a permanent mark had the course pursued been 

 in conformity with Mr. Guppy's very interesting sugges- 

 tion. That there is a rich field awaiting detailed investi- 

 gation in connection with the fascinating subjects opened 

 up by Mr. Guppy will be admitted by most naturalists. 



In glancing back at the early seed-structures one is 

 struck with the complexity of their organisation as com- 

 pared with the relative simplicity of modern seeds. The 

 pollen-chamber, the large elaborate integument, and the 

 complicated vascular arrangements, so characteristic of the 

 Pteridosperm seed, have for the most part passed away, 

 giving place to much simpler structures. Occasional ex- 

 ceptions no doubt occur ; the seeds of Palms have remark- 

 able integuments, whilst those of Magnolia, some Aroids, 

 Sapotaceae, &c., show an unusual development of vascular 

 tissue. Most astonishing of all perhaps is the integu- 

 mental tracheal sheath which closely invests the nucellus 

 of Cassytha.' Though evidence of their precise function be 

 lacking, the fact that many of these structures belong to 

 the tropical forest makes closer knowledge desirable. For 

 in these localities the conditions must have long been 

 relatively stable ; thus increasing the chance that the struc- 

 tures referred to still perform their pristine functions. 

 These and other cases like them need elucidation, but to 

 the broad statement that the seeds of recent Spermophytes 

 are organised on simple lines there can be no question. 

 This reduction in complexity may be accounted for on two 

 grounds. In the first place fertilisation by motile sperms 

 has been replaced by fertilisation by pollen-tubes. Instead 

 of sperms being discharged into an internal water-chamber 

 upon which the archegonia abutted, the male cells are 

 carried through .soft tissues to the egg in a plastic tube. 



In other spheres the like befalls. If primitive man had 

 occasion to journey from Baker Street to Waterloo, he 

 penetrated the forest and then swam the river ; to-day his 

 descendants are projected from the one to the other with 

 accuracy and despatch in a subterranean passage. 



Just at what stage the improvisation of the pollen- 

 chamber gave place to the newer method we have no 

 knowledge. Perhaps some information on this point may 

 emerge from Dr. Wieland's exhaustive researches into the 

 extensive Yale collections of American Cycadeoideas. For 

 the Bennettiteaa already show a simplification of the seed 

 in certain respects ; though, owing to the late stages of 

 development usually found in European examples, this point 

 could be cleared up. 



The other cause that must have played a prominent part 

 in the simplification of the seed was the association with 

 it of other structures which relieved it of a part of the 

 original load of duties that fell to its lot. The dense heads 

 of 'Bennettites show us this, and the same may be said 

 of most Coniferous strobili. But the Angiospermic ovary 

 provides the best example of a special organ inclosing the 

 seed or ovule, affording it protection during the immature 

 stages and also collecting the pollen. The steps by which 

 this came about remain hidden, and any discussion of the 

 matter is of course premature. The carpels mav have 

 been derived from reduced sporophylls or from portions of 

 sporophylls that were more closely associated with the 

 seeds. The cupule of Lvginodendron is an organ rather 

 suggestive in this connection. One is tempted to compare 

 it with a rudimentarv ovary, playing the serviceable part 

 of a moist air-chamber for the seed during the earlier 

 stages of its development. 



However, the origin of the fruit and of the flower, with 

 all its manifold organs, must be left to the future : they 

 form no part of our theme. Some day a happy discovery 

 will yield a clue, and the reproach that we are in entire 

 ignorance of the affinities of the dominant phylum will be 

 removed. 



1 'M. Mirand-, " Le d<?veIop. el la 

 q^ s^r. hot., torn, ii., igos. 



:. d. Cassylhacies," Ann. d. Sc. Nat.. 



NO. 192 1, VOL. 74] 



The history of the seed, as I read it from the imperfect 

 and fragmentary data that are available, has been a series 

 of advances spread over long geological periods. The 

 possibilities of the seed-habit were realised only bit by bit, 

 and the high efficiency of the modern seed depends in large 

 degree upon the close association of other structures which 

 cooperate in its functions. No doubt the first step, the 

 retention of the megaspore, was the most important of 

 all ; though, that this might be effective, some contrivance 

 for the capture of the pollen-grains must have accompanied 

 it. Later steps in the process of seed-evolution would 

 include the adjustnient of an intraseminal embryonic stage, 

 and in time the substitution of the pollen-tube for the 

 liberation of sperms. 



Now assuming, as I think we are entitled to assume, 

 that seeds have come into existence along some such lines 

 as those thus crudely blocked out, there is a great difficulty 

 in conceiving the process other than discontinuous. Every 

 one of the stages emphasised involves the conception of 

 something more abrupt than mere gradual variation. And 

 there is, of course, the old difficulty confronting us as to 

 how the organ or mechanism came to be preserved at its 

 inception. AH these difficulties vanish when it is recog- 

 nised that effective variation is of the discontinuous order, 

 and that the successive changes involved may be consider- 

 able enough to be designated jumps. Happily such views, 

 based upon experimental results, have been formulated by 

 De Vries in his Mutation Theory. That theory is so well 

 known to botanists in this country that any exposition here 

 is quite superfluous. The least thing that can be said in 

 its support is that it is perfectly tenable. But we may go 

 much further than that. Apart from the Theory of 

 Natural -Selection, no modern hypothesis of evolution has 

 been so helpful or so likely to stimulate further work. 

 The results of continued investigations in this field, now 

 so actively pursued, will be awaited by all biologists with 

 a keen and sympathetic expectancy. Not the least of the 

 advantages that follow in the wake of the Mutation Theory 

 is the shortening of the time required for the evolutionary 

 process. .As the physicist imposes a time limit to the 

 period during which life has been possible on the earth, 

 a working theory that reconciles the demands of the 

 biologist with the physical limitations is decidedly re- 

 assuring. In this connection it is very interesting to note 

 that Monsieur Grand 'Eury, one of the most active and 

 distinguished workers in the field of pal.xobotany, should 

 have found data supporting the view of mutation.' In 

 tracing the passage of fossil plants through great thick- 

 nesses of rock he has been impressed on the one hand with 

 the high degree of permanence of certain forms, and on 

 the other with the suddenness, when the moment came, 

 with which one species passes into another. 



The collection of data of this kind from our own Coal 

 Measures appears to me a very pressing necessity in view 

 of the rapidity with which the coalfields are being 

 exhausted. Indeed, the present is an unique opportunity 

 which can never recur, and the chance of systematically 

 utilising it is slioping away. Whatever view one may hold 

 as to the expediency of making exhaustive collections of 

 the recent flora, there can be no two opinions of our 

 manifest duty to " make hay while the sun shines " in 

 the matter of the coal fossils. Regarded as systematically 

 arranged collections showing how the plants occur in 

 definite localities, the contents of inost of our museums, 

 as I am assured by competent authorities, are practically 

 worthless. That innumerable specimens of the greatest 

 value are preserved in museums may be readily conceded ; 

 but my point is that these collections have been made 

 without system, and that details of precise locality and 

 horizon are frequently wanting. All this has to be done 

 over again, and I believe local societies working in touch 

 with a central organisation could do a memorable service 

 which would earn them the gratitude of future generations 

 and at the same time provide a fresh outlet to their 

 energies. 



To us the coal industry, with its vast resources, is a 



convenient mechanism for making fossil plants accessible. 



The colliery proprietor may be relied on to afford all 



reasonable facilities for the 'acquisition of select examples 



1 Grand'Eurv, CoiiiMcs yendits. trm. cxlii p 55. 



