318 Transactions. — Botany. 



tural seeds are especially responsible for the majority of our 

 most common weeds, and I have given an example of this 

 in the first paper read by me before this Institute.* 



It is evidently the case that weeds of cultivation, such as 

 chickweed, shepherd's purse, groundsel, &c, must have de- 

 veloped their special characteristics within comparatively 

 recent times — that is to say, they have developed them pari 

 passu with the development of cultivation of the land by the 

 human race. This, from the naturalist's point of view, does 

 not point to any great antiquity. 



An examination of any list of the naturalised plants of a 

 district — for example, that of the plants of Port Nicholson by 

 the late Mr. Kirk.f or that of our <^wn immediate neighbour- 

 hood issued a couple of years ago by the Dunedin Field 

 Club — reveals certain interesting general facts. Thus all, or 

 nearly all, are capable of self-fertilisation, if they are not 

 habitually self-fertilised. If one looks at the weeds in any 

 unkept bit of garden-ground at the present midwinter season 

 (July), they will probably find some or all of the following 

 species producing seed in abundance from flowers which never 

 open and which are more or less imperfect in structure : 

 Shepherd's purse (Capsella bursa-pastoris), winter -cress 

 (Barbarea vulgaris), bitter-cress [Gardamine hirsuta), hedge- 

 mustard (Sisyinbrium officinale) , wart-cress (Senebiera didyma), 

 chickweed (Stellaria media), mouse-ear chickweed (Gerastium 

 glomeratum and G. triviale), groundsel (Senecio vulgaris), sow- 

 thistle (Sonckus oleraceus), spurge {Euphorbia peplus), and 

 perhaps various others. This faculty of producing more or 

 less imperfect self-fertilised flowers is almost an essential 

 feature in all such plants, many of which are thus enabled to 

 produce fruit at all seasons of the year, and almost inde- 

 pendent of the weather. It is perhaps the most character- 

 istic feature about them. Another point is that most of them 

 produce very small and very numerous seeds ; and still 

 another, that a large proportion of them come to maturity 

 very rapidly, and that their seeds germinate quickly. These 

 characters are all retrogressive from one point of view — that 

 is to say, the plants exhibiting them have tended to become 

 less instead of more specialised in their development ; but by 

 this degradation of their reproductive organs they have really 

 become better adapted for the peculiar conditions which are 

 imposed upon them in their struggle with the gardener and 

 agriculturist. 



(4.) I am not aware that any plants naturalised within 

 historic times have been introduced by means of either wind, 



* Trans. N.Z. Inst., vol. ix., p. 538. 

 t Trans. N.Z. Inst., vol., x., p. 362. 



