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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



of the Lily family, as Yucca, Cordyline, and Dracaena; Pandanus, 

 Bavenala, and XanthorrJioea of other families pretty well complete 

 the Hst. 



On the other hand, the largest dicotyledonous trees, as the Gum 

 trees and Wellingtonia, have small leaves, while arborescent species 

 are many. 



Another characteristic feature of Monocotyledons is the parallel 

 venation of the leaf -blades, as of tulips, hyacinths, grasses, sedges, &c. 

 But the supposed or so-called blade is really, i.e. homologously, the 

 petiole only, no true blade being formed in these plants. 



The condition results from the scattered condition of the vascular 

 cords in the stem. A number of these near the circumference pass 

 outward and enter the sheathing base of the leaf and then run parallel 

 or slightly curved to the top. 



If a blade be formed at all, the first type is an oval termination to 

 the parallel-veined basal part produced by their curving outwards. 

 The next form is a spear-shaped blade, caused by the outer veins curv- 

 ing downwards. The third stage is seen in the arrow-head form; the 

 next is to have the space filled in so that the petiole is now attached to 

 the blade in the middle, which becomes peltate, but this name is 

 better applied to the blade when it is rounded as in the Lotus, and 

 our pennywort. 



These forms can be seen in the germinating Victoria and in the 

 arrowhead. These are both aquatic plants ; but similar forms are seen 

 in many of the Arum family which are terrestrial, as in Arum macu- 

 latum of our hedgerows. 



These types of blade acquire reticulations or a netted-veined struc- 

 ture, imitating, but not altogether identical with, those of Dicotyledons, 

 the cause of the differences being that water has interfered so as to pro- 

 duce degradations, and the net-veined types of certain Monocotyledons 

 show the effort made to adjust the blades to the same aerial conditions 

 as those to which blades of dicotyledonous leaves are adapted. Thus 

 a Monocotyledon has, as a rule, no solid mid-rib like that of a Dicoty- 

 ledon. If such be required for strength a cluster of separate cords are 

 crowded together ; then as the blade widens each in turn deviates right 

 or left, till there may be none left to reach the apex of the blade. 

 This can easily be studied in the leaves of Arum macidatum, 

 especially in the first formed, elliptical blades — presumably survivals of 

 a floating type. Attempts to form a cordate blade with a rounded 

 summit often occur in this plant. 



Degeneracy in the Reproductive Organs of Monocotyledons. — The 

 first and most obvious feature in flowers is that while the floral whorls 

 are usually in fours or fives in Dicotyledons, they are only in threes in 

 Monocotyledons. These numbers result from their leaf arrangements. 



When a plant has opposite and decussate " leaves — that is the two 

 leaves of each pair stand at the same level or node, and the pairs next 

 above and below are at right angles to them — then, if this is carried up 



