58 HEV. G. HEXSLOW HOMOLOGY AND 



axis being terminated by a tuft of perfect and imperfect anthers ; 

 the petals, and the two carpels of the flower, having been atrophied 

 or arrested. 



He notices how the calyx, corolla, pedicels, and receptacles 

 vanish by degrees : the stamens which remain being then enveloped 

 by the concave bract, which takes the place of the calyx. The 

 bracts of ditferent flowers thus approximating each other, assume 

 the form and structure of anthers, always however retaining a part 

 which recalled the foliaceous nature of the bract.* 



That bracts should ever assume a pistilloid character is, a priori, 

 still more unlikely, as being further removed from the central 

 organ of a flower. Dr. Masters has, however, described f a mal- 

 formed Lolium 2^erenne, in which the flowering glumes had styles 

 and stigmas ; the essential organs being absent, but replaced by a 

 tuft of minute scale-like bodies, some of which were prolonged into 

 styliform processes, the sexual organs being otherwise suppressed. 



In a proliferous case of Delphinium elatum, described and figured 

 by Cramer,! the parts of the flowers were metamorphosed into 

 rudimentary carpels. The axis was elongated and terminated above 

 in one case by a similar abortive flower ; in another by an umbell 

 of such flowers, every part of which was more or less carpellary ; 

 while all the bracts on the prolonged axis, even those out of the 

 axis of which the branches of the umbell sprang, were similarly 

 made of open and rudimentary carpels. 



III. Axr.ix AXD AppEjrDiCTJLAii Strtjcttjiies. 



The organs of plants have hitherto been considered as either 

 caulomes or phyllomes ; but Homology proceeds a step further and 

 recognises a common origin for both. 



That leaves and stems are homologous is a probability that finds 

 support in the following facts. 



1. The elements of a leaf are a continuation of those of the stem, 

 only spread out so as to acquire a new form in order to sustain a 

 new function. The petiole is very frequently concave above, when 

 the fibro-vascular bundles are mostly open or horse-shoe-shaped ; 

 but in terete or cylindrical petioles, the circles are closed and then 

 there is no appreciable difference between them and a stem. With 

 regard to the blade, though the fibro-vascular bundles are not 

 usually closed cylinders as in stems, yet when leaves acquire a 

 terete form as in Sedum and other CrassulacecB, they resemble 

 stems. 



2. Leaves can produce buds like stems; (1) normally, as Brijo- 

 j)hyllum caUjcitmm and many ferns ; and (2) abnormally, as in 

 artificial propagation of Begonia, etc. 



3. Leaves can develope roots as in the above methods of 

 propagation. 



* ' Bull. Soc. Bot. Fr.,' tome xiv, p. 253. 



t ' Journal of the I;innean Society,' Botany, vol. vii, p. 121. 



X ' Bildungsabweichungen,' etc., Heft i, taf. 10. 



