K.— BOTANY. 241 



meiosis as reconstituting the daughter-nuclei, he suggests that the 

 greatest importance of the reduction-division lies rather in its making 

 nevf combinations of chromosomes possible. He points to the difference 

 between only one reduction in each cycle, as in the simplest organisms, 

 and many, as in those that have achieved a higher development ; and he 

 concludes that the origin of a large diploid sporophyte is thus an advan- 

 tageous biological organisation, since it secures many reduction-divisions, 

 and consequently niimerous new combinations. This hypothesis has the 

 advantage of giving a general explanation of the origin of a diploid 

 sporophyte, independently of any special circumstances of life under which 

 it came into being. 



Devonian Fossils and a Land Flora. 



We may here leave aside any detailed study of alternation in the 

 Thallophytes, though it is full of interest, and the investigation of it rich 

 in promise ; particularly that of the Brown Seaweeds, as last year's 

 proceedings of the Section have shown. This year we may concentrate 

 on the Land Flora, and inquire how recent discoveries may have affected 

 our outlook on it. Notwithstanding that the years since 1894 have been 

 marked by discoveries of the first rank, I see no reason to alter my belief 

 in an interpolated sporophyte in the Archegoniatse, except in respect of 

 the primary causality ; nor do I relinquish the view that the two genera- 

 tions are homoplastic and not homogenetic. Indeed, the new evidence 

 appears to me to strengthen rather than to oppose the position previously 

 stated. I see no need materially to modify the biological reasoning which 

 T offered in 1890 in explanation of the formal difference in Land-plants 

 between the alternating generations, nor the recognition of the stabilising 

 influence of the amphibious life upon them. But the new discoveries 

 have altered the aspect in certain particulars, and in nothing more than 

 in the relations of the Bryophyta to the rest. 



The most impressive event of recent times in the sphere of morphology 

 has certainly been the recognition and constitution of a new class of 

 vascular plants. The disclosure of the fossils of the Rhynie Chert, of 

 early Devonian age, is not only notable as introducing in unusual detail 

 a type of vegetation barely hinted at before, but also because those early 

 land-plants present material of the highest importance for comparison. 

 The new class of the Psilophytales was founded to receive them, together 

 with the old Devonian fossil Psilophyton, and some others ; while their 

 relation to the li^^ng Psilotacese is recognised. These rootless plants 

 together present a new facet upon the problem as to the origin of members 

 in vascular plants, though they do not wholly resolve it. Apart, however, 

 from such conclusions as the new facts may suggest, they introduce a 

 tonic effect into morphology. Something positive is actually seen, and 

 of very early existence, as a set-off against reasoning from data so often 

 isolated and insufficient, or even purely imaginary. For a balanced 

 statement on land-vegetation viewed in the light of the newly acquired 

 facts one cannot do better than refer to Chapter VI of Dr. Scott's book on 

 ' Extinct Plants and Problems of Evolution,' 1924. Discussing the 

 relation of the Bryophytes to other Archegoniatae, he remarks how Kidston 

 and Lang had pointed out that the three phyla, Pteridophyta, Bryophyta, 

 1920 R 



