TRANSACTIONS OF SECTION K. 1027 



the parts classed under these several heads were held to be homoloyous. In their 

 definition all those characters which refer to function were put aside, the definitions 

 relating to origin and relative position ; the reproductive organs were grouped 

 with the rest, with the result that these parts were described as bearing a varying 

 morphological value. But this purely formal morphology is now dead ; it long 

 survived a mere passive belief in evolutionary views, but their active practice has 

 strangled it. The first step towards emancipation was the recognition of sporangia 

 as parts sid (/enevis, Eichler, agreeing with Brauu and Strasburger, found it 

 * highly probable according to the theory of descent ' that such a structure as the 

 ovule has universally the same morphological dignity. It remained for Goebel to 

 make the general statement that sporangia stand in a category by themselves, and 

 are probably not the result of modification of any vegetative part. It was in this 

 way that tlie phylogenetic factor was first asserted as bearing on a question of 

 importance in the morphology of plants. Adherents of descent no longer passively 

 accepted the direct results of investigation ; they began actively to check and control 

 the interpretation of them ; but this position was not attained till more than twenty 

 years after the publication of Darwin's ' Origin of Species.' Since then, however, 

 views as to descent have taken an increasingly important place in the province of 

 morphology, till at the present moment a far-reaching comparison of allied forms, 

 assisted by experiment, is the most potent instrument in the hands of the morpho- 

 logist. 



But various writers admit in varying degree this factor of comparison as con- 

 trolling other considerations. There is indeed a wide range of difl'erence on this 

 point. I will cite only two extreme views. On the one hand is the view of 

 Strasburger, which he enunciated so early as 1872. The enthusiasm for evolution 

 in the Jena school found its botanical expression in the aphorism, ' The highest 

 problem of morphology is to explain the form of plants, but this problem can only 

 be solved genealogically.' This statement is repeated in a more definite form in 

 Strasburger's text-book : ' Phylogeny is thus the only real basis for morphology.' 



At the other extreme is the method of physiological organography put forward 

 by Sachs in his Lectures. I am aware that he subsequently modiiied his views ; I 

 merely quote the system which he propounded in 1882, as being the antithesis to 

 that of Strasburger. For in the physiological organogi-aphy descent is hardly 

 taken into account at all ; parts which are plainly of distinct origin by descent are 

 classed together. This organography of Sachs, though introduced with all its 

 author's charm of style, never convinced the botanical world, for it treated plant-, 

 too much as the creatures of present circumstance. It may be taken as illustratmg- 

 the extreme reactionary swing of the pendulum from the non-physiological attitude 

 of the formal morphologists ; a protest against the exclusion of function from the 

 morphological arena. The protest was salutary, but its form was extravagant. 



Let us now consider whither ' phylogeny, as the only real basis of morphology,' 

 may lead us. Let us take as our provisional view that homology in the strictest 

 sense implies repetition of individual parts, in successive generations, just as the 

 hand of the child repeats in position and qualities the hand of the mother. Though 

 among seed-bearing plants, for instance, this repetition may apply for the plant- 

 body as a whole, it will be at once apparent that such repetition as regards the 

 individual is found in comparatively few cases in plants. The continued embryo- 

 logy of all the higher forms, the indefinite number of the parts successively 

 produced, and the variety in detail of their arrangement show that in the strictest 

 sense repetition of individual parts cannot be traced. In a pan of seedlings of 

 the Sunflower, raised from seed of the same parent, the cotyledons in all cases 

 may be regarded as homologous in the strictest sense, as they correspond in origin, 

 number, position, and form to like parts in the parent. In a similar way the first 

 root of the seedling appears to be individually identical with the first root of the 

 parent, or of any other seedling of the batch. In those plants in which a foot or 

 suspensor is present occupying a constant position with regard to the parts of the 

 embryo, it will not be doubted that within near lines of affinity the foot in any 

 one specimen corresponds to that of any other. The exact repetition which is thus 

 found to exist may be regarded as the most complete type of homology. 



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