446" FOURTH GROUP. SEED-PLANTS. 



reaches a very considerable size, as in Aesculus, Quercus, Cas/anea, Juglans, Cucurbita> 

 T?'opaeolum, Phaseolus, Faba ; in small seeds however it is of proportional size, as in 

 the Cruciferae, Compositae, Rosiflorae, etc. The absence of endosperm is generally 



due to its displacement by the rapid growth of the 

 embryo before the seed reaches maturity ; it is only in 

 a few cases, as in Tropaeolum and Trapa, that the 

 endosperm is rudimentary from the first ; in Nymphae- 

 aceae and Piperaceae the embryo and the endosperm 

 surrounding it continue small, the rest of the space 

 inside the seed-coat being filled with perisperm. 

 FIG. 374. chimonanthusfragans. A The embryo in parasites and saprophytes destitute 



transverse section of the fruit before it is 



quite ripe. B longitudinal section of the of chlorophyll and with small seeds is usually very 



same, f the thin pericarp, e remains of the . 



endosperm, c cotyledons, c embryo taken small and continues undifferentiated till the seed is 



from the seed, showing the cotyledons . t t 



wrapped round each other with the ex- ripe I in MOnOtrOpd it COntamS Only frOHl five tO 



tremity of the root below. . 



nine cells, and even in Pyrola secunda which contains 



chlorophyll it has only from eight to sixteen cells (Hofmeister) ; the ripe 

 seeds of the Orobanchaceae 1 , Balanophoreae and Cytineae 2 , etc., contain a very 

 small undifferentiated embryo in the form of a roundish mass of cellular tissue; 

 the embryo of Cuscuta is indeed comparatively large and long and has a root 3 , 

 but its root is remarkable for showing no sign of a root-cap. The embryo of 

 some species of Cuscuta also has no rudiments of leaves. Viscum on the other 

 hand, one of the Loranthaceae, a parasite but with abundance of chlorophyll, 

 has a large and well-developed embryo. In plants also that are not parasitic the 

 differentiation of the organs in the embryo is sometimes imperfect. The embryo of 

 Uiricularia 4 for instance shows no rudiment of a root ; as the plant subsequently 

 developes no roots, it behaves in this respect -in exactly the same way as Salvinia, 

 which is also a water-plant (p. 234) and forms no rudimentary root in the embryonic 

 stage. On the other hand the embryo of Utricularia is provided with a large number 

 (11-13) of rudimentary leaves of a peculiar character. 



If the embryo in a ripe seed is differentiated, as it usually is, it consists of an axis 

 and two opposite first leaves, between which the axis terminates as a naked vegetative 

 cone, as in Cucurbita or sometimes as a bud with several leaves, as in Phaseolus^ 

 Faba (Fig. 376), Quercus, etc. ; instead of two opposite cotyledons a whorl of three 

 leaves is not unfrequently found in plants which normally have only two (Phaseolus, 

 Quercus , Amygdalus and many others) 5 . The opposite cotyledons are usually of similar 

 form and of the same size ; but in Trapa one is much smaller than the other, and 

 there are even isolated cases in which there is only one cotyledon ; this is the case in 



1 Koch, Ueber d. Entw. d. Samens von Orobanche (Jahrb. f. wiss. Bot. XI). On Ctiscuta see 

 Hanstein in Bot. Abhandl. Bd. II. Heft 3. 



2 Solms-Laubach, Ueber d. Bau d. Samen in d. Familien d. Rafflesiaceae u. Hydnoraceae (Bot. 

 Ztg. 1874). 



3 The root performs its functions for a short time only, that is only until the seedling plant has 

 succeeded in rinding a host ; then the root and the whole of the lower part of the plant dies off, and 

 the rest of the plant lives on its host without any connection with the ground. 



* Kamienski, Vergl. Unters. ii. d. Utricularieen (Bot. Ztg. 1877, p. 701). 

 5 For numerous other cases see Bot. Ztg. 1869, p. 875. 



