378 EXTKACTS AND ABSTEACT8. 



An abnoniifil structure met with in Leiinminonct and Cucurhitacett, 

 and c'staLlishfd by Janczewski as a fourth type, is rcjiarded by the 

 ])resent author simply as an exhibition of degeneration. Here the 

 tip of the radicle of the embryo before germination is normal, but 

 directly sprouting commences, the line of division between Periblem 

 and Dermatogcn, and between Dermatogen and root-cap is effaced. 

 Owing to longitudinal growth of the central cells of the cap, a more or 

 less evident median columnar portion (siiule) is found ; and this is 

 sometimes seen even before sprouting of the radicle. Contempo- 

 raneously with the loss by these cells of their plasmatic contents, the 

 formative Dermatogen and Periblem-cells cease to dii'ide radially, and 

 80 to produce cells for formation of the body of the root. In many 

 instances the formative cells cease dividing tangentially and producing 

 the cap. Still, under these circumstances, the vegetative point can 

 long retain its normal appearance, e.g., in Rumex, Epilohium, and 

 Helianthus. The power of tangential division remains with the top 

 cells of the Periblem, but they develope, not layers wbich continue 

 the regular Periblem-curves, but longitudinal rows of cells which join 

 the rows of the central column and take on their character. 



A remarkable exception to the dicotyledonous type consists in the 

 Periblem taking a share in the construction of the cap : this is found 

 in the genus Acacia. In the radicle of the embryo of yi. galiophylla 

 the Dermatogen shows no tangential division of its cells ; moreover, 

 it entirely covers the cap, which arises here, as in Gymnospermous 

 roots, from the Periblem. Further, on the occurrence of germination, 

 a column (sliule) is formed in the centre of the cap as in the type. 

 In A. lophantha the cap is very large, and the Dermatogen sometimes 

 divides tangentially, by which means the outer layer takes on the 

 character of epidermis, and in this case, too, a " siiule " is formed. 

 The root-tip of Juglaiu comports itself in a similar way, but here the 

 greater part of the cap is derived from the Dermatogen, and only a 

 small part from the Periblem. 



Among Monocotyledons the independent cap-forming " Calyp- 

 trogcn " is so widely diffused as to justify Janczewski's erection of 

 the ordinary root of this class into a special type, but the author does 

 not think that Janczewski should be followed in basing a second 

 monocotyledonous type on Hydrocharis and Pistia. The Dermatogen 

 is here laid down through the first tangential division of the formative 

 cells, and henceforward it follows its special law of development, 

 appearing either single or divided in the form of a many-layered 

 (two-layered in Iru) epidermis. In only a few cases is the Derma- 

 togen to be distinguished from the first of the Periblem-curves when 

 the latter arc developed in the centripetal sense ; but where a many- 

 layered centrifugally developed epidermis is found, the first-differen- 

 tiated Dermatogen can be shai'[)ly distinguished from the outer-formed 

 layers of Periblem. In many cases the outer part of the epidermis 

 passes gradually into the inner, but sometimes this gradual transition 

 is interrupted by the development of the latter centrifugally, and of 

 the former centripetally. 



As in Dicotyledons, a " siiule " is usually found here, but it appears 

 later than in Dicotyledons, and sometimes is not to be seen. In the 

 case of Cordyline vivij)ara the top of the body of the root participates 

 in its formation. 



