DICOTYLEDONS. 



557 



space enclosed by the testa, and thus, when ripe, often attains a very considerable 

 size {e.g. Aesculus, Juglans, Cucurbita, Tropseolum, Cupuliferse, Leguminosse, &c.) ; 

 though in small seeds it still remains of moderate dimensions (as in Cruciferse, Com- 

 posit;^, Rosiflorae, &c.). The absence of endosperm generally results from its 

 absorption by the rapid growth of the embryo before the ripening of the seed; 

 only in a very few cases is it rudimentary from the first (Tropieolum, Trapa). In 

 Nymphaeaceae and Piperaceae the embryo and the endosperm which surrounds 

 it both remain small, the rest of the space within the testa being occupied by 

 perisperm. 



The Embryo generally attains but very small dimensions in the small-seeded 

 parasites and saprophytes destitute of chlorophyll, and remains without differentiation 

 until the time of ripening of the seed ; in Monotropa it never consists of more than 

 two cells, and even in Pyrola secunda, which possesses chlorophyll, only of from eight 

 to sixteen (Hofmeister). The ripe seeds of Orobanche, Balanophora, Rafflesiacea^, 

 &c., contain a very small undifferentiated embryo in the form of a roundish mass of 

 tissue ; the embryo of Cuscuta is of moderate size and length, but the formation of 

 leaves and roots on the filiform stem^ is suppressed. The mistletoe (Loranthaceee), 



I-ir,. \o\—Chivio}ianthus/ra):ians: A liorizontal section of the nearly ripe fruit: B longitudinal section of t/ie 

 saine.ytlie tliin pericaqi. e reni.-iins of the endosperm, c cotyledons; C the embryo removed from the seed, showing 

 the cotyledons rolled round one .nnother, the radicular end below. 



on the other hand, parasitic but containing chlorophyll, produces an embryo which 

 is not only large but well-developed. 



If the embryo of the ripe seed is differentiated, as is generally the case, it 

 consists of an axis and two primary opposite leaves (cotyledons) betvv^een which the 

 axis terminates as a naked vegetative cone (Cucurbita), or bears a bud which sometimes 

 consists of several leaves ( Vicia Faba, Fig. 405, Phaseolus, Quercus, &c.). Instead 

 of the two opposite cotyledons, a whorl of three is not unfrequently formed in those 

 plants which normally possess only two" (Phaseolus, Amygdalus, Quercus, &c.). 

 The opposite cotyledons are usually alike in form and vigour; in Trapa however 

 one remains much smaller than the other ; and cases even occur in which only one 

 has been formed, as in Ranunculus Fican'a^, where it remains below in the form of 

 a sheath, and in Bulbocapnos, a section of Corydalis. The two cotyledons generally 

 form by far the larger part of the ripe embryo, so that the axis has the appearance 



» According to Uloth (Flora i860, p. 265) the root-cap is also absent. On parasites see 

 especially Solms-Laubach in Jahrb. fiir wissensch. Bot. vol. VI, p. 599 et ^eq. 



■' Numerous additional instances are given in the Bot. Zeitg. 1869, p. 875. [Masters, Vegetable 

 Teratology, Ray Soc 1869, p. 370.] 



2 Irmisch, Beitr"ge zur vergleichendcn Morphologic der Pfianzen, Halle 1S54, p. 12. 



