TRANSACTIONS OF SECTION K. 1035 



the Vascular Cryptogams at all,' and that ' there is no appreciahle resemblance 

 between the fruit of any of the Bryophyta and the plant of any Vascular Crypto- 

 gam,' and the suggestion has been thrown out afresh that they may really be 

 ' degenerate descendants of higher forms.' 



In view of statements such as these it may be well to examine the Bryophyta 

 quite separately, without reference to Vascular Plants at all, and see what are their 

 main bearings on theories of alternation. And if the Bryophytes were the only 

 Arcbegoniate Plants in the world, I think the case for their origin by a progressive 

 antithetic alternation would be an uncommonly strong one ; the points which are 

 especially noteworthy are : (1) The readiness with which they may be arranged in 

 natural sequences which illustrate increasing vegetative complexity of the sporo- 

 phyte as a consequence of progressive sterilisation ; (2) the nuclear details, which 

 are as yet known, however, in only few cases ; (3) the constancy of the two 

 alternating phases, the relations of which are very seldom disturbed by apospory, 

 and never, to my knowledge, by apogamy. 



The first of these matters has been dealt with at length in my ' Studies.' It is, 

 of course, possible for any one to read such sequences as are there mentioned in 

 reverse order, and to uphold a theory of simplification ; but this must be shown 

 to be in accordance with probability. Now it appears to me that the general 

 probability in the case of the Bryophytes is against simplification, for the larger the 

 number of spores which can be matured the greater the probability of survival ; 

 even in cases where, as in Buxbaumia and Diphyscium, there is an exiguous, and 

 probably reduced Moss-plant, the sporogonium is not of a reduced type, but, on 

 the contrary, unusually large. It seems to my mind much more probable that the 

 Bryophytes as a whole illustrate a course of progressive complexity. A comparison 

 of anatomical details frequently suggests a progressive sterilisation, a process which 

 we see demonstrated both in Pteridophytes and Phanerogams, where actual con- 

 version of potentially sporogenous tissue into temporary or permanent vegetative 

 tissue does occur. When it is added that the nuclear evidence, scanty though it 

 still is, shows the sporophyte with a double number of chromosomes, and the 

 reduction taking place on the tetrad division of the spores, the comparison with 

 the segmented zygotes of Algse and Fungi above mentioned seems inevitable. The 

 position of those who hold views of antithetic alternation will, therefore, be that 

 the simple sporogonium was produced as a post-sexual growth. The starting-point 

 was probably some such multicellular body as we see nowadays in certain Algie and 

 Fungi resulting from division of the zygote, but not necessarily homogenetic with 

 any such body that we know now living. The land-habit imposed a restriction on 

 fertilisation, and an alternative method of increase in numbers was an advantage. 

 The multicellular body resulting from division of the zygote provided the means 

 for this ; the cells developed separately as dry, dusty spores. As the number of 

 divisions increased, the powers of the plant to nourish, protect, and disseminate the 

 spores became the measure of the number produced. Hence followed the elabora- 

 tion of the nourishing and disseminating mechanism, which has involved a divert- 

 ing of some cells from their first office of spore-production, the start being, perhaps, 

 made in a manner similar to tlie formation of the peridium in the UredineoB. To 

 my mind — taking the Bryophyta alone — there is an inherent probability in all 

 this which far counterbalances any of the obstacles which have been raised 

 against it. 



The greatest obstacle is the fact of apospory in Mosses. This departure from 

 the usual alternation will be more generally discussed in relation to the Ferns, where 

 it is more frequent. Besides its being artificially induced in Mosses by special 

 treatment, it appears also to have been noted by Ugo Brizi in Nature, in the case 

 of atrophied capsules of Funaria, which had buried themselves in the soil. The 

 essential point is the production of the sexual generation by direct vegetative 

 growth from the neutral. This would appear to involve a reduction of chromo- 

 somes, but Pringsheim's drawings show nothing analogous to the usual process of 

 tetrad division to form the spores ; the reduction, if it occurs, must be eflfected in 

 some other way. 



A theoretical suggestion on this^point will be made later. Meanwhile let us 



