ANGIOSPERMS. MONOCOTYLEDONS. 



43 1 



leaf; but in the Helobiae the axial portion forms the larger part of the embryo 

 (niacropodous embryo). The rudiment of the primary root is at the posterior end of 

 the axis, and near it in the Gramineae are the rudiments of two or more lateral roots, 

 which like the primary root arc enclosed in a 

 root-sheath (Fig. 355). The embryo of the 

 Gramineae is further marked by having an 

 outgrowth from the axis beneath the cotyledon, 

 which envelopes the whole of the embryo like 

 a mantle and forms a thick peltate plate on 

 the dorsal side, where it is in contact with 

 endosperm ; this outgrowth is known as the 

 scutellum. In the Orchideae, Apostasia and 

 Burmanniaceae the embryo in ripe seeds is 

 still a roundish undifferentiated body, in which 

 the plumule is not formed before the com- 

 mencement of germination *. 



In germination 2 either the roots begin at 

 once to elongate, and their emergence in the 

 Gramineae ruptures the sheath which envelopes 

 them and which remains attached to the axis 

 as the coleorhiza, or, which is more commonly 

 the case, the lower part of the cotyledon 

 elongates and pushes the radicular end with 

 the plumule enveloped by the sheath of the 

 cotyledon out of the seed (Fig. 356), while its upper part remains as an organ of 

 suction in the endosperm till the food contained in the latter is exhausted : in the 

 Gramineae the whole of the plumule issues from the seed, the scutellum only 

 remaining in it to convey the food-material of the endosperm to the embryo. 



The primary root of the Monocotyledons soon ceases to grow, even though it 

 may develope strongly during germination, as in Palms, Liliaceae, Zea, etc. ; its place 

 is taken by lateral roots, which spring from the axis and are stronger the higher up 

 they are formed in it. The Monocotyledons have therefore no persistent root-system 

 developed from the primary root, like that of Gymnosperms and many Dicotyledons ; 

 sometimes indeed no roots are ever formed, as is the case in some saprophytes without 

 chlorophyll among the Orchideae, as Epipogum and Corallorhiza. 



The plumule of the embryo is in most cases completely enclosed in the first 

 sheath-like leaf, the cotyledon, which either developes into a sheathing scale-leaf, or 

 becomes at once the first green foliage-leaf of the young plant, as in A Ilium. There 

 is usually a second leaf present within the cotyledon, in the Gramineae even a third or 

 fourth, which lengthen by intercalary growth at their base and emerge during 

 germination from the sheath of the cotyledon ; these and the succeeding leaves are 

 stronger, the later they are formed on the growing axis, which usually continues very 

 short during germination and forms no distinct internodes, as in Alliitm, the Palms 



sr 



F'G 355. Longitudinal section of fruit of Zea Mais 

 c rind of the fruit, n appendage of the stigma, fs base of the 

 fruit, eg yellowish firm part of the endosperm, ew its white 

 and looser part, sc the scutellum of the embryo, ss its tip, 

 e its epithelium, k the plumula, iu (below) the primary root, 

 ms root-sheath, TV (above) secondary roots springing from 

 the first internode of the primaiy stem sf. Magn. about 

 six times. 



1 No primary root is developed in the Orchideae even in germination. 



2 See Sachs in Bot. Ztg 1862 ancl 1863. 



