IN ANGIOSPERMAE 155 



cultivated in pots. It is possible that the Japanese have obtained their forms of 

 Retinispora by cultivation in pots, accompanied by root-pruning, whereby they have 

 hindered through unfavourable conditions the appearance of the adult form. 



The behaviour of only two other genera of conifers in which the organs of 

 vegetation are especially diverse will be mentioned here. 



4. Phyllocladus \ The species of Phyllocladus are distinguished by their leaf- 

 like twigs, phylloclades, standing in the axils of small scale-like leaves which, 

 originally green, soon become withered and brown. These scale-like leaves are 

 merely transformed primordia of foliage-leaves and they are, as it were, a middle 

 stage between the normal occurrence in the Coniferae and that which is seen in 

 Pinus, where the leaves on the chief-stem are from the outset brown scales. The 

 first leaves of the first annual shoot of the seedling, as well as a portion of those 

 which are developed in the second year, are flat green needles ; at the end of the 

 shoot they are much shorter ; and on the third annual shoot they are much more 

 like the scale-leaves of the older plant, and into these they gradually pass. The 

 phylloclades too only gradually acquire their striking leaf-like configuration, and 

 occasionally their extremity develops into a cylindrical twig clad with leaves arranged 

 spirally. A ' fixation ' of the juvenile form has not yet been tried. 



5. Sciadopitys. The germination in this genus is quite like that of Pinus, 

 but at a later stage it forms its peculiar double needles, not spur-shoots. After the 

 two linear-lanceolate cotyledons foliage-leaves appear on the short first annual shoot 

 of the seedling plant. These leaves are simple with an undivided apex and have a 

 simple vascular bundle. Upon the next annual shoot the leaves are reduced, as 

 is the case in Pinus, to scales and in their axils in the upper part of the shoot 

 are developed the characteristic double needles with retuse apex and having 

 two vascular bundles. 



5. ANGIOSPERMAE. 



The differences in the construction of the juvenile and the adult 

 form are in general the greater the more different are the external 

 conditions to which they are severally adapted 2 , whilst if these do not 

 operate, the primary leaves, with which we have here at first to deal, are 

 only arrested formations a , if they are specially different from those which 

 follow, and their differentiation is then simpler. Thus the primary leaves 

 are simple in the trifoliate species of Trifolium and in Ononis and other 

 genera, and this primary form of leaf is retained for a very long time in 

 Ononis Natrix. Kennedya rubicunda has primary leaves without trace 

 of pinnules, then follow leaves in which pinnules are laid down but 

 are reduced to small pointlets 4 ; on succeeding leaves pinnules are 



1 II. Th. Geyler, Einige Bemerkungen iiber Phyllocladus, in Abhandl. d. Senckenb. Nalurf.- 

 Gesellsch., xii (iSSi), p. 209. 



2 See what has been said on page 144. 



3 As I have shown to be the case in the ferns, see page 152. 



' This is also observed in the lowermost pinnules in old plants of Acacia lophantha, which 

 I mention here because it shows the phenomenon is one of arrest. 



