Chai\ XXVI. KELATIVE POSITION OF PAKTS. 337 



interior and exterior florets in certain Cornpositous and 

 Umbelliferous plants, is due to the pressure to which the 

 inner florets are subjected ; but this conclusion is doubtful. 



The facts just given do not relate to domesticated produc- 

 tions, and therefore do not strictly concern us. But here is 

 a more appropriate case : H. Miiller 12 has shown that in 

 shortfaced races of the dog some of the molar teeth are placed 

 in a slightly different position to that which they occupy 

 in other dogs, especially in those having elongated muzzles ; 

 and as he remarks, any inherited change in the arrangement 

 of the teeth deserves notice, considering their classificatory 

 importance. This difference in position is due to the shorten- 

 ing of certain facial bones and the consequent want of space ; 

 and the shortening results from a peculiar and abnormal state 

 of the embryonal cartilages of the bones. 



Relative Position of Flowers with respect to the Axis, and of Seeds 

 in the Ovary, as inducing Variation. 



In the tr irteenth chapter various peloric flowers were described, 

 and their production was shown to be due either to arrested 

 development, or to reversion to a primordial condition. Moquin- 

 Tandon has remarked that the flowers which stand on the summit 

 of the main stem or of a lateral branch are more liable to become 

 peloric than those on the sides ; 13 and he adduces, amongst other 

 instances, that of Teucrium campanidatum. In another Labiate 

 plant grown by me, viz. the Galeohdohn luteum, the peloric flowers 

 were always produced on the summit of the stem, where flowers are 

 not usually borne. In Pelargonium, a single flower in the truss is 

 frequently peloric, and when this occurs I have during several years 

 invariably observed it to be the central flower. This is of such 

 frequent occurrence that one observer 14 gives the names of ten 

 varieties flowering at the same time, in every one of which the 

 central flower was peloric. Occasionally more than one flower in 

 the truss is peloric, and then of course the additional ones must be 

 lateral. These flowers are interesting as showing how the whole 

 structure is correlated. In the common Pelargonium the upper 

 sepal is produced into a nectary which coheres with the flower- 

 peduncle; the two upper petals differ a little in shape from the 

 three lower ones, and are marked with dark shades of colour ; the 

 stamens are graduated in length and upturned. In the peloric 



12 " Ueber fotale Rachites," ' Wiirz- I3 ' Terjtologie Veg.,' p. 192. 



burger Medicin. Zeitschnft,' 18G0, B. u 'Journal of Horticulture,' July 



i. s. 265. 2nd, 1861 *• 253. 



VOL. II. Z 



