INTRODUCTORY ESSAY. XXXVI 
state of our knowledge they are not of practical application. Such are—1. The relative number and 
extent of genera, the limits to whose species it is difficult to assign, owing to the variableness of their 
. organs.—2. The number of species which materially vary by altering their form and habit during 
different periods of their growth, and of those whose variations seem independent of age, climate, or 
condition. 
There are many minor considerations that are equally well worthy of study with the above, but 
which can only be treated of in detail, and studied by local botanists; such as variation im size, sta- 
ture, colour, and many other particulars which do not produce any generally admitted difficulty in 
recognizing species. 
1. The genera whose species are extremely variable are— 
Of very general distribution, 45 :— 
Clematis. Taraxacum. Gaultheria. Parietaria. Pelargonium. 
Ranunculus. Lobelia. Polygonum. Dodonzea. Sonchus. 
Linum. Euphrasia. Hypericum. Senecio. 5 gen. Cyperaceæ. 
Geranium. Cardamine. Apium. Calystegia. 10 gen. Grasses. 
Oxalis. Rubus. Olea. Potamogeton. 
Epilobium. Wahlenbergia. Urtica. Veronica. 
Gnaphalium. Plantago. Gentiana. Luzula. 
Endemic, or of confined geographical distribution, 84 :— 
Pittosporum. Pimelia. Oreomyrrhis. *Carmichelia. Microtis. 
Coriaria. Oreobolus. Oraspedia. *Tupeia. Weinmannia. 
Cassinia. *Hoheria. Trophis. Ozothamnus. * AIseuosmia. 
Elatostemma. Leptospermum. Aristotelia. Leptocarpus. Parsonsia. 
Pterostylis. Dracophyllum. Coprosma. Elzeocarpus. Calorophus. 
* Anisotome. Prasophyllum. Ourisia. Leptinella. Calceolaria. 
Celmisia. *Phormium. Thelymitra. Santalum. 
(a.) The first obvious result of this classification is the great number of variable genera, amount- 
ing to 79 out of 282, or upwards of one-third ; and that the more or less local genera are rather more 
variable than the widely diffused ; for I find in the whole flora that those genera common to all guar- 
ters of the globe are to those confined chiefly to Australia and Tasmania as 182 to 150, or nearly one- 
half of the whole flora: whereas the variable local genera are to the variable widely distributed in 
the proportion of 34 to 45. As, however, the division into local and peculiar genera is somewhat 
arbitrary, and that into variable and constant much more so, these conclusions are necessarily vague. 
Perhaps a more intelligible comparison may be made by examining the absolutely endemic genera. 
Of these there are 27, or one-tenth of all the genera in the flora, and six only (or one-fifth) of these 
are very variable ; whence it would appear that there is absolutely less tendency to vary, amongst the 
endemic genera, than amongst those more widely dispersed. 
(5. With regard to the widely diffused genera that are variable in New Zealand, most of 
them are so in all quarters of the globe, but present little uniformity in amount of variation ; 
thus Rubus, of which there is only one in New Zealand, and that an extremely variable species, 
has very few representatives in Australia, and those not particularly variable ; very many in 
* Those marked with an asterisk are either absolutely peculiar to New Zealand, or found elsewhere in Norfolk 
Island only, as Phormium; or in Lord Auckland's Group, as Anisotome. 
