THE ANGIOSPERMAE 1583 



also influence their form, as is well seen in Myristica. The endosperm in 

 these large seeds is ruminate and the cotyledons during germination 

 become markedly lobed, the lobes growing into the corresponding lobes 

 of the endosperm. The same absorptive function has obviously influenced 

 the cotyledons of endospermic Monocotyledons, notably in Grasses. 



Cotyledons practically never have stipules. The seedling of Fagopyrum 

 is unique in that the cotyledonary node bears an ochreal sheath surrounding 

 the plumule, though it is absent from other polygonaceous seedlings. The 

 ochrea here is common to the two cotyledons. In other genera connate 

 union of the cotyledons is not uncommon, the bases being united into a 

 sheath around the plumule. Petiolate cotyledons, e.g., Psidium (Guava), 

 may also be united by the edges of the petioles, so forming an elongated 

 tube. Fusion of cotyledons will be dealt with later. 



Because one or two familiar seedlings like those of Vicia faba have 

 buds in the cotyledonary axils, it is not generally realized that this is 

 actually an uncommon condition outside the Papilionaceae and that in 

 most cases of their occurrence their further development is inhibited by 

 the growth of the plumule. There are cotyledonary buds in Liniim and they 

 form the normal renewal shoots of perennial species of that genus in the 

 second year. In Galimn there are serial buds, three or four in the axil of 

 each cotyledon, and these develop freely and form part of the normal branch 

 system. 



Inequality of the cotyledons may develop inside the seed or it may 

 appear during germination. The seeds of Peperomia show interesting stages 

 in the evolution of heterocotyly due to the specialization of one cotyledon 

 as a haustorium while the other remains epigeal. 



Almost invariably the two cotyledons arise oppositely at one node, 

 below which is the primitive axis or hypocotyl and above which is the 

 epicotyl arising from the plumular bud. Only rarely is there an internode, 

 or mesocotyl, between the cotyledons. The hypocotyl varies greatly in 

 length. In big dicotyledonous seedlings [Riciniis, Helianthiis) it may be a 

 foot in length. In a great many Monocotyledons it is very short and not 

 infrequently tuberous. Tuberosity of the hypocotyl is common also in 

 Cruciferae, Ranunculaceae and some Monocotyledons. In Cruciferae it 

 forms the greater part of the "roots" of Turnip and Radish (Fig. 1443). 

 At the lower end the hypocotyl passes directly downwards into the primary 

 radicle. The point of junction, the collet of French anatomists, is usually 

 distinguishable, but in the tuberous forms mentioned above, the external 

 transition is often gradual and difficult to locate exactly. The hypocotyl is 

 part of the stem, although a specialized part, and has normally the structure, 

 epidermis and colouring of a stem, but the level of anatomical transition, 

 the junction between stem structure and root structure, is not always at 

 the collet. In some cases the transition takes place at intermediate levels 

 in the hypocotyl, with no change in external appearance and, on the con- 

 trary, it sometimes occurs below the collet, the stem anatomy persisting 

 downwards some way into the radicle. Normally the hypocotyl does not 

 s 



