140 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



11 pentastichous " or five-ranked foliage,* starting from an embryo with 

 two cotyledons. 



AY hen one cotyledon is wanting, nature appears to have adopted a 

 different method. Thus it has been discovered that in Asparagus and 

 Tamus the first leaf is situate just over the site of the missing or rudi- 

 mentary cotyledon. Then the second and third leaves are in a plane at 

 right angles to that in which the cotyledon and first leaf stand, 

 8 



thus : 0.1 cot. These three appear to lay the foundation of a tri- 

 2 



stichous arrangement, as in Carex, by slightly shifting the positions : 

 8 the three ranks being at an angular distance of 120°. A 



1*4 b* similar shifting occurs in making the trimerous whorls of 

 £ the flower, and we arrive at it thus : — 



3 



6 



1 5 

 4 



2 



That nature has the power to "shift" the "insertion" of leaves 

 may be seen, for example, in the common Laurel. In the horizontal 

 boughs coming from the side of the bush the leaves are " distichous " 

 13 5 7 



— g- 1 g g but on a vertical shoot issuing from the top of the 



bush, the leaves are " pentastichous," the sixth being in the same vertical 

 line as the first on the spiral line passing through the numbers q 

 1 to 6. 5 



AYith regard to the development of the foliage, if we compare 4 

 that of Victoria regia with Sagittaria sagittifolia, a remarkable 8 

 similarity will be observed. The first leaves of the former are 2 

 incompletely developed ; they have no limb at all ; that of the next * 

 has a lanceolate blade, the third has a hastate, the fourth a sagittate, then 

 comes an orbicular blade ; and in Nclumbiuiii a peltate one is finally 

 acquired. 



Sagittaria begins with a ribbon-like phyllode in deep water ; then a 

 spathulate extremity indicates the commencement of a blade. This 

 becomes hastate, then sagittate. The further stages are not reached in 

 that plant ; but the orbicular is found in Frogbit, and hastate-peltate in 

 Caladium. 



There are several other points of agreement between the morphology of 

 aquatic Dicotyledons and Monocotyledons, which all tend to afibrd an 

 accumulation of probabilities that this latter class has been descended 

 from aquatic forms of the former. It is quite impossible to say when and 

 from what plants it took place, but it is interesting to see that the late 

 Robert Brown (facile princeps among botanists) actually put Cycads 

 among Monocotyledons in his " Prodromus." For further details I must 

 refer the reader to my paper elsewhere, t 



* " The Origin of the Prevailing System of Phyllotaxis," Trans. Linn. Soc. 2nd ser. 

 vol. i. p. 647. 



t "A Theoretical Origin of Endogens from Exogens through Self-adaptation to 

 an Aquatic Habit," Journ. Linn. Soc. vol. xxix. 



