K.— BOTANY. 239 



true.' But after reference to the fossil evidence, as it then was, he con- 

 ■cluded that it is more probable that the higher Cryptogams came direct 

 .from plants of the nature of Algae than from Bryophyta or any plants at 

 .all like them ; he added, however, that ' this view is pure hypothesi.s.' 

 It must, of course, be remembered that these quotations from Dr. Scott's 

 * Evolution of Plants ' (p. 225) were of pre-Ehynie date. A luminous 

 .statement of his later views was contained in his address to Section K in 

 Edinburgh in 1921, which will be in the memory of you all. 



Church, in his vivacious essay on ' Thalassiophyta ' (1919), went much 

 further than this guarded and scientific statement by Scott of 1911. By 

 ■' deduction from types still existent in the sea ' he assumes ' Algae of the 

 transmigration ' as a bridge between the vegetation of land and sea. His 

 transmigrant Algae ' appear, in fact, to have been more highly organised 

 than any single algal type at present known to exist in the sea,' and ' to 

 jhave combined the best features, as factors of the highest grade of pro- 

 .gression, of the known great conventional series of marine phytobenthon, 

 -and yet to have belonged to none of them.' He boldly fills the gap that 

 puzzles us all by hypothetical organisms that no one has seen, and which 

 he expressly tells us we shall never see {I.e., p. 88). If the discussions of 

 the 'nineties were inconclusive engagements at long range, what is this ? 

 It is certainly not that closer analysis advocated by Bateson. 



An alternative to such an effort of imagination may be found in the 

 -examination of organisms that really exist, or are known to have existed, 

 illuminated by the conception of homoplasy, or, as it is often called, 

 parallel-development. The comparisons should be based upon the 

 recurrent fact of the chromosome-cycle, since this underlies the ontogeny 

 •of all plants that show sexuality. Somatic development in sexually 

 produced organisms is seen to be in some measure independent of the 

 •successive events in the chromosome-cycle. The somata may be uni- 

 •cellular, existing only as potential gamete or zygote respectively ; they 

 need' not necessarily be alike in themselves, nor need they appear at the 

 .same points in the cycle. For instance, it is found that the pennate 

 Diatoms have diploid vegetative cells, while in the centric Diatoms they 

 are haploid, this latter state being shared by the vegetative cells of the 

 Desmideae and Zygnemese. That a soma should appear at the same 

 ipoint in the cycle of two or more organisms does not necessarily prove 

 that they have had the same phyletic history. The full proof that they 

 ■did can only follow from the observation of sequences of close relationship, 

 Tvhich should indicate the successive steps to have been the same if a true 

 homogeny exists. We are, in fact, thrown back upon close comparative 

 •observation for tracing truly homogenetic sequences of somatic develop- 

 jnent, rather than upon the mere position of a given soma in the cycle, 

 ■or the recognition of its diploid or haploid state. Until such evidence is 

 available it will be best to hold it as possible that the origin of any somata 

 •compared has been homoplastic. 



Some such view as this was clearly in the mind of Professor Oltmanns 

 dn 1923 {Morph. und Biol, der Algen, vol. iii, p. 143). Speaking with the 

 fullest knowledge of the cytologically distinct alternation as it appears in 

 the Algae, he says : ' When we affirm that an alternation of a gametophyte 

 ;and a sporophyte is seen in the more highly developed Algae, that is not 



