218 Linnaan Society. 



ternal coat. Their earliest indication is in the form of tubercles, 

 through the investing covering of which these rootlets burst a pass- 

 age, in all respects similar to the coleorhiza in the germinating em- 

 bryos of Monocotyledonous plants. The coleorhiza is sometimes 

 extended to some distance along the rootlet, but in other cases it 

 forms merely a swelling round its base. The same appearance, 

 although far from general, was observed by St. Hilaire in the ger- 

 minating embryos of numerous other exorhizal plants, as Myosurus, 

 Plantago, Valerianella, Urtica, Senecio, Sonchus, Calendula, Matri- 

 caria, Veronica, Phaseolus, Medicago, &c. In TropcEolum the radicle, 

 although exorhizal, exhibits a kind of valve-like opening for the exit 

 of the plumule, which has been called a coleorhiza : and a somewhat 

 similar appearance is said to occur in the germination of the seed of 

 Viscum albiiyn ; this, however, Mr. Miers apprehends can refer only 

 to the coleorhizal mode of bursting of the attenuated expansion of 

 the thin covering of the albumen which is spread over the growing 

 radicle. 



Dr. Allemao, Mr. Miers adds, here considers the radicle of the 

 embryo as forming part of the caulicle or stem, and the root as ori- 

 ginating in the subsequent growth of the embryo, after it is released 

 from its integuments, and produced by the expansion of the obtuse 

 extremity of the radicle, which he calls the " gommo ;" and Gaudi- 

 chaud the 7-adiciilar bulb. This view was taken by Turpin nearly 

 twenty years ago, and represented by him, in the germination of 

 Solanum tuberosum (Mem. Mus. xix. p. 19. t. 1), where all the radi- 

 cular portion of the embryo is referred to the tigelle or ascending 

 system, while the true root is represented as beginning from its 

 sprouting point in the radicular bulb. It has not, however, been 

 generally countenanced, and Mr. Miers states that he cannot per- 

 ceive that it has any advantages over the more generally received 

 theory which regards the radicle as an elementary root, commencing 

 from the point of union of the cotyledons and their junction with 

 the plumule. On the contrary, it is disproved by numberless facts, 

 and more especially by one to which he lately called the attention 

 of the Society, in the germination of the embryo ol Xanthochymus , as 

 figured by Dr. Roxburgh ; in which (in addition to the principal root 

 thrown out at the base of the seed, at the point which Dr. Allemao 

 would call the radicular bulb) another secondary root is seen pro- 

 ceeding from the summit of the nucleus out of the ascending collar 

 or tigelle, immediately below the scales, which appear to be minute 

 cotyledons, showing that the main body of the nucleus or radicle 

 belongs to the descending system of the root. It is more natural, 

 Mr. Miers thinks, to conclude, in the case cited by Dr. Allemao, 

 that the main descending shoot, growing out of the radicular bulb, 

 and also tlie subsequent coleorhizal rootlets, are productions of that 

 axile portion of the radicle, which Mr. Miers has called the ncorhiza ; 

 and under this point of view he considers it easy to account for the 

 coleorhizal character of the secondary rootlets in the germination of 

 Ceratocephalus, as described by St. Hilaire. A very singular example 

 of this sort of production is shown by Klotzsch, in the germination 



