INTRODUCTORY ESSAY. XXXIX 
much. Enough has been adduced to show that this subject is most difficult and obscure, and I may 
add that it is one in which hasty generalization from first impressions has given rise to much error. 
2. Genera whose species alter in form or habit. These are—Hymenanthera, Pittosporum, Plagi- 
anthus, Melicope, Discaria, Edwardsia, Carmichelia, Ackama, Panag, Aralia, Carpodetus, Coprosma, 
Parsonsia, Olea, Weinmannia, Dammara, Thuja, Podocarpus, Dacrydium, Phyllocladus, Rhipogonum. 
Many of the above vary so remarkably that botanists have been greatly puzzled by the abnormal 
forms they present: thus a state of Hymenanthera crassifolia has been referred to Goodenia, one 
species of Weinmannia has been made into two genera, and an Olea has been converted into a 
Metrosideros. Some states of Plagianthus urticinus and of Carpodetus serratus (plants of two very 
different Natural Orders) are almost undistinguishable, and so are Hymenanthera crassifolia and 
Pittosporum obcordatum; so also Melicytus micranthus, Panag anomala, and Melicope simplex, 
are often so extremely like one another in foliage as to be confounded when in a dry state. With 
regard to Carmichelia, Ackama, Weinmannia, most of the Araliacee, Coprosma, Parsonsia, and 
some of the Pines, the variation is greatest in amount between old and young plants; but with 
Discaria, Hymenanthera, Pittosporum, some species of Coprosma, Olea, and many Pines, there seems 
to be no law, abnormally formed organs appearing on the same branches with normal ones. 
From the above list it would appear that variability of this nature is most frequent amongst 
more or less endemic genera and species, but whether in this respect the New Zealand Flora is more 
variable than others I have not proved. The Yew, Cedar, Holly, Ivy, and especially Furze and 
Juniper, perhaps vary in Europe as much as, or more than, the above; but it is difficult to appre- 
ciate the amount of variability in a familiar object. On the whole I am inclined to think that the 
New Zealand Flora is remarkable for the number of plants which vary thus, but that this peculiarity 
is rendered conspicuous by the prevalence of Conifere and Araliacee, which are variable in all parts 
of the world. 
