ANGIOSPERMS. DICOTYLEDONS. 451 



lateral root enclosed in a coleorhiza is formed beneath the primary axis of the embryo, 

 and persists with it, while the primary root and the first leaves perish. Among the 

 numerous cases of this kind may be mentioned also Physalis Alkekengi, Mentha arvensis, 

 Bryonia alba, Polygonum amphibium and Lysimachia vulgaris \ The formation of 

 bulbs is not unknown in Dicotyledons, as in some species of Oxalis, though it does not 

 occur so frequently as in Monocotyledons ; tubers occur more frequently as swellings 

 of underground branches, stolons or thick or slender rhizomes. The great majority 

 of Dicotyledons are subterranean perennial plants, and send up periodically leafy and 

 flowering shoots which die down at the close of each period of vegetation. In all such 

 cases, if the primary root-system of the young plant perishes, new roots are repeatedly 

 produced from portions of the stem ; and the power which most Dicotytedons possess 

 of forming roots from the stem when kept moist and in the dark permits their 

 propagation from almost any branch or portion of a branch. Some, as Hedera Helix, 

 climb by means of roots issuing constantly from the stem which is slender and 

 needs support ; others like Fragaria send out runners to a distance, the bud on 

 which developes into a new plant, and the stem thus produced sends roots into the 

 ground, and so on. The order of development of new roots from the stem is 

 generally acropetal throughout the class, but they usually make their appearance at 

 some distance behind the growing bud ; in many Cactaceae however they may arise 

 close to it. 



The branching. In connection with the branching of Dicotyledons it is 

 necessary to distinguish between radial and dorsiventral organs. In radial organs 

 the normal monopodial branching is axillary; the lateral shoots arise in the angle 

 formed by the median plane of the leaf and the internode above it ; at least one 

 lateral shoot is formed in the axil of each leaf on the vegetative stem, though many of 

 these axillary buds remain latent. Other shoots are sometimes formed in a longi- 

 tudinal row above the true original axillary shoot, as for instance above the axils of 

 the foliage-leaves in Aristolochia Stpho, Gleditschia and Lonicera, above the axils of 

 the cotyledons in Juglans regia and of the developed cotyledon in Trapa, In woody 

 plants the axillary bud destined to live through the winter is often so grown round by 

 the base of the leaf-stalk that it cannot be seen till after the fall of the leaf, as in the 

 case in Rhus typhinum, Virgilia lutea, Platanus, etc. ; these are termed inirapetiolar 

 buds. Besides the ordinary axillary branching a few cases of lateral and monopodial 

 but extra-axillary branching are known in Dicotyledons; to these belongs the 

 formation of the tendrils of Vilis and Ampelopsis^ which appear according to Nageli 

 and Schwendener beneath the growing point of the mother- shoot, opposite to and a 

 little later than the youngest leaf; in Asclepias syriaca and some other plants a 

 vegetative lateral shoot is formed beneath the terminal inflorescence between the 

 insertions of the foliage-leaves, which themselves subtend axillary shoots. 



In dorsiventral organs on the other hand the branching is usually extra-axillary 2 . 

 Branched dorsiventral organs which are of very common occurrence in Thallophytes, 

 Muscineae and Ferns are rare in the vegetative region of the Dicotyledons. The 



1 The above is taken from Irmisch's full accounts in his Beitr. z. Vgl. Morphol. d. Pflanzen, 

 Halle, 1854 and 1856, in Bot. Zeit. 1861 and elsewhere. 



3 Goebel, Ueber d. Verzweigung dorsiventr. Sprosse (Arb. d. Bot. Inst. z. Wurzburg, Bd. II, 

 Heft I). 



Gga 



