436 PHANEROGAMS, 



A. CYCADEy^\ 



The Embryo, enclosed in the large endosperm, possesses two opposite unequal 

 Gotyledonary leaves, which lie with their inner surfaces face to face, cohering 

 towards their apices. The tendency of the subsequent foliage-leaves to branch is 

 sometimes displayed even in these cotyledons, a rudimentary lamina being formed 

 on the larger one, with an indication of pinnae (as in Zamia, Fig. 313 B'). The 

 seed germinates when laid in moist earth, but only after a considerable interval ; 

 the testa splits at the posterior end and allows the emission of the primary root, 

 which at first grows vigorously downwards, but sometimes assumes afterwards a 

 tuberous form or produces a system of thicker fibrous roots. According to Fig. 313 

 C borrowed from Schacht, and a more recent statement by Reinke, the branching 

 of the primary root is laterally monopodial ; Miquel, however, asserts the existence 

 of bifurcations of the more slender roots in older plants of Cycas glaiica and Ence- 

 phalartos, which is also confirmed by Reinke's investigations into the history of their 

 development. By the elongadon of the cotyledons which remain in the endosperm 

 and absorb their nourishment from it, their basal parts and the intermediate plumule 

 are pushed out of the seed. The portion of the axis which bears the cotyledons, 

 as well as that which developes above them, remains very short, but a consider- 

 able lateral increase of size takes place beneath the apex due to a large develop- 

 ment of parenchymatous tissue. The stem thus acquires the form of a roundish 

 tuber which it retains even at a later period in some species ; but in most it 

 lengthens in the course of years into an erect tolerably stout column which some-' 

 times attains a height of some metres. This slow increase in height, together with 

 the considerable increase in thickness of the growing end, is correlated with the 

 absence of a tendency to branch as in other similar cases (Isoetes, Ophioglossum, 

 Aspidium Filix-vias, &c.). The stem of Cycadeae usually remains perfectly simple, 

 although old stems sometimes divide into branches of equal stoutness. But when 

 several flowers are formed at the summit, this evidently depends on branching ; and, 

 as far as one is able to judge from drawings, it is probable that this branching 

 is dichotomous. In old or sickly plants small bulbous or tuberous gemmae are not 



' Miquel, Monographia Cycadearum, 1842. [Ditto, On the Sexual Organs of the Cycadaceoe ; 

 Journ. of Bot. March and April 1869.] — Karsten, Organogr. Betracht. iiber Zamia muricata, Berlin 

 1857. — Mohl, Bau des Cycadeen-stammes (Vermischt. Schrift. p. 195). — Mettenius, BeitrJige zur 

 Anatomic der Cycadeen (Abhandl. der kiinigl. Sachs. Gesellsch. der Wissensch. vol. VII, i86r). — 

 [W. C. Williamson, Contributions towards the history of Zamia gigas, Trans. Linn. Soc. vol. XXVI, 

 1870. — Carruthers on Fossil Cycadean Stems from the Secondary Rocks of Britain, ibid.'\ — On 

 the structure of the pollen see Schacht, Jahrb. fiir wissensch. Bot. vol. II, p. 142 et seq. — Kraus, 

 Ueber den Bau der Cycadeenfiedern (Jahrb. fiir wissensch. Bot. vol. IV). — Reinke in Nachrichten der 

 konigl. Gesellsch. der Wissensch. in Gottingen, 1871, p. 532. — De Bary, Bot. Zeitg. 1870, p. 574. — 

 Juranyi, Bau u. Entwickelung des Pollens bei Ceratozamia (Jahrb. fiir wissensch. Bot. vol. VIII, 



