44^ FOURTH GROUP.— SEED-PLANTS. 



reaches a very considerable size, as in Aesculus, Quercus, Casianea, Juglans, Cucurbifa, 

 Tropaediim, Phascolns, 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. 

 ■/ The cjnbryo in parasites and saprophytes destitute 



quite ripe. B lonffitudinai section of the of chlorophyll aud wlth Small sccds is usually ver^' 



same, ythe thin pericarp, e remains of the ^ ' 



endosperm, <: cotyledons, c embryo taken suiall aud contiuues Undifferentiated till the seed is 



from the seed, showing the cotyledons 



wrapped round each other with the ex- rjpe ; in MoHotropa it contains only from 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 \ Balanophoreae and Cytineae "^ etc., contain a very 

 small undiff"erentiated 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 ^, 

 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. Vise urn 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 

 Utricularia * 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)^ 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 



^ Koch, Ueber d. Entw. d. Samens von Orobanclie Jahrb. f. wiss. Bot. XI). On Cuscuta see 

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



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

 Ztg. 1S74). 



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

 succeeded in finding 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- 7°0- 



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



