726 Hens low .— The Origin of Monocotyledons from Dicotyledons , 
leaves are always scale-like or are mere sheaths ; while in all Dicotyledons 
perfect leaves are developed. 5 1 
The primary leaves of the seedlings of Victoria regia , however, are 
similarly more or less arrested in development, and are comparable with 
those of Sagittaria? 
It might be suggested that Cycas , like Palms with a similar pseudo- 
pectinate or compound leaves, was derived from an aquatic ancestor, but 
now become a strong xerophyte, like Agave and A toe, which are com¬ 
parable in form with Stratiotes Aloides. But, on the other hand, intense 
drought may bring about an imitative result, as in Hakea (Proteaceae). 
This has more probably been the case with Cycas. These ‘ pectinate 5 leaves 
of xerophytes closely resemble in form the submerged leaves of Pro - 
serpinaca paiustris. 
Ceratozamia is the only known Cycad with only one cotyledon, though 
the second can be, and has been developed. The ovules are shed shortly 
after fertilization, so that the cotyledon is not developed until the seed lies 
on the ground. It arises at one, the lower, side, and gradually enlarging, 
the margins touch each other with the sheathing base. It thus agrees 
with hygrophytic and hydrophytic plants of both classes, as well as 
terrestrial Monocotyledons. 
A longitudinal section shows a ‘ scale 5 opposite to the cotyledon, just 
as in the Oat. An inequality in size appears to be not unusual in other 
Cycads, as it is also in Nymphaea. 
The reason why the lower cotyledon, i.e. as the seed lay on the soil, 
was only developed was clearly not in consequence of gravity, which would 
act equally on the development of both, but lies in the presence of water, 
whereby the lower one gets more saturated. When arrangements are 
made so as to equalize the moisture all round the seed, and it is made to 
germinate on the clinostat, both cotyledons are developed. Rotation is 
found to retard the growth. According to the figures given the primary 
root is very slender, and adventitious roots are represented as issuing from 
the hypocotyl close to the cotyledon. 3 
1 4 In ntrinque longitudinals, plus minus obvius, cotyledonum duorum aceretionem indicat, 
earumque separatio interna in regione Plumulae ante germinationem certe conspicuae manifesta est. 
4 In hoc ordine igitur habemus, saltim respectu structurae externae Embryonis, transitum a Mono- 
cotyledonibus ad Dicotyledones. Plumulae autem evolutio cum priori classe magis convenit; in his 
omnibus enim, Gramineis Aroideisque exceptis, foliola primaria hujus organi semper abortiva et 
squamiformia, vel merae vaginae sunt; dum in Dicotyledonibus omnibus folia perfecta evadunt. 
Aliud discrimen forsan obtinet inter Plumulas duarum classium ; in Dicotyledonibus ejusdem foliola 
primaria cum cotyledonibus alternant [as in Tamils and Asparagus , which have rudimentary second 
cotyledons]. In Gramineis et Aroideis contra in quibus solummodo e Monocotyledonum Classi 
hanc determinare possumus, cotyledoni opponuntur. Cycadeae quantum e re tam minuta judicare 
liceat, hac ratione cum Dicotyledonibus quadrant ’ (Prodromus Florae Novae Hollandiae, p. 347). 
It will be noticed that Brown wrongly uses the word cum. It only means 4 with’ in the sense 
of c accompaniment ’. 2 loc. cit., p. 515. 
3 Morphology of Gymnosperms, by Coulter and Chamberlain, pp. 99 ff., Figs. 75-9 ; Figs. 187- 
