620 PHANEROGAMS. 



and pushes the end of the root, together with the plumule which is enveloped 

 by the sheath of the cotyledon, out of the seed (Fig. 419), while its upper part 

 remains in the endosperm as an organ of absorption, until the endosperm is 

 consumed. In Grasses, however, the whole of the plumule projects from the seed, 

 the scutellum only remaining behind in it, in order to convey to the embryo the 

 food-material contained in the endosperm. 



The growth of the primary root of Monocotyledons soon ceases even when 

 it is very strongly developed during germination, as in Palms, Liliacese, Zea, &c.; 

 lateral roots are produced in its place, springing from the axis, which are stronger 

 the higher up they are produced on it. No such permanent root-system is 

 developed from the primary root of Monocotyledons as is found in Gymnosperms 

 and in many Dicotyledons; sometimes no roots at all are produced, as in some 

 Orchidaceous saprophytes destitute of chlorophyll (as Epipogiurn and Corallorhiza), 

 which never possess any roots. 



The plumule of the embryo is usually completely enclosed in a single 

 sheath-like structure, the first leaf or cotyledon, which developes either into a 

 sheath-like cataphyllary leaf or at once into the first green foliage-leaf of the 

 young plant (as in Allium). Within the cotyledon there is generally a second 

 and sometimes (in Grasses) a third and fourth leaf, which protrude on germination 

 out of the sheath of the cotyledon, increasing by intercalary growth at their base ; 

 these and the leaves which are formed subsequently are larger the later they are 

 formed on the growing axis. The axis usually remains very short during germi- 

 nation without forming any distinct internodes {Allitmi, Palms, &c.), or it lengthens 

 more rapidly and becomes segmented into evident internodes (Zea and other 

 Grasses). 



The increase in strength of the plant may take place by the powerful growth 

 of the axis of the embryo itself, so that this at length forms the primary stem 

 of the mature plant bearing the organs of reproduction, as for instance in most 

 Palms, Aloes, Zea, &c. If the axis of the embryo remains short while it increases 

 in strength, it may grow considerably in thickness and form a tuber (Fig. 420), 

 or, if the bases of the leaves become thick (as in Allium Cepa), a bulb. If the 

 axis of the embryo itself developes into the primary stem, whether into an upright 

 one or a creeping rhizome, it first of all takes the form of an inverted cone, which 

 is elongated or abbreviated according to the length of the internodes. This 

 peculiarity, which belongs to most Monocotyledons in common with Ferns, depends 

 on the absence of any subsequent increase in thickness; the portions of the stem 

 first formed retain their size, while each successive portion is larger ; the diameter 

 of the stem is therefore so much larger the nearer it is taken to the apex. As 

 long as this growth proceeds, the stem continues to grow stronger ; but sooner 

 or later there comes a time when every portion of the stem acquires the same 

 thickness as the previous one ; the stem then becomes cylindrical, or, if it is 

 compressed like some rhizomes, still with a uniform breadth. The lateral shoots 

 exhibit the same peculiarity when they spring low down from the primary stem 

 (as in Aloe, Sec). But the primary shoot which springs from the embryo not 

 unfrequendy disappears after producing lateral shoots which grow more vigorously 

 than it, and these again transfer the further growth to new shoots, which now 



