NATURAL SCIENCES OF PHILADELPHIA. 189 



same condition of feet is found in that species. The feet, indeed, are larger 

 than those of exiUpes, and the tarsi, particuhirlj, are long; but the toes are 

 still notably short, in a relative sense, not having increased pari passu with 

 enlargement in other respects. I would attempt to explain this fact in the 

 same way. 



So far as I know, the claws of j^Egiothus have not been modified coincident- 

 ally with those changes that have made the several races what they are. The 

 claws of exiUpes and canesccns, indeed, are longer, compared with the toes, than 

 those of other forms ; but this a relative, not absolute difference. The claws 

 of all the species are liable to vary within rather wide limits, — this discrepancy 

 belonging clearly, however, to the class of individual peculiarities. 



The conclusions to be drawn from the foregoing facts are obvious. We have 

 seen that canescens, the form most strongly differentiated at present, is also the 

 one most easily accounted for by the operation of certain known laws that 

 produce variation in species. If this were not a separate and independent 

 creation, it must have been evolved at some time out of Unarms. The ques- 

 tion of its specific distinction, then, is merely a question of time ; we can only 

 say that it has divaricated further than any other known forms from the 

 original standard, and that, though it has reached a point where most orni- 

 thologists would draw a dividing line qua species, yet it is reallj' only a va- 

 riety of Unarms. A fortiori, in the case of all the other above described modifi- 

 cations of Unarius, we have varieties, not species. Simply, they have not 

 progressed so far in the process of differentiation ; they either began to be 

 modified later, or the modifying influences have not been so effectual towards 

 that end. But if canescens is a " species," so also is each of the others. There 

 are only involved differences in degree, not in kind. 



The Law of Development in the Flowers of AMBROSIA AETEMISI.EFOLIA. 

 BY THOMAS MEEHAN. 



In the fruit of Ambrosia artemisixfoUa the perigynium is crowned with a 

 series of horns. I propose to show that these are all that remains of other 

 flower buds, which have been absorbed by their elder sister during infancy. 



It is not generally known that this species is occasionally dioecious, though 

 Dr. Darlington in his Flora ce.itrica makes note of the fact ; nor is it known 

 to the mass of botanists that a peculiar form of neutral flower exists, though 

 many years ago Torrey & Gray (Flora of North America) briefly alluded to it. 

 These dioecious forms and neutral flowers afford the key to the whole struc- 

 ture. 



In the regular form of this species the sequence of the flowers is according 

 to the laws recently developed in my papers on sex. The female flowers re- 

 ceive the plants' first and greatest care, and always appear in the lines of 

 strongest vitality, of which a vigorous axial development is one striking type. 

 The male flowers only appear in the weaker lines, after the cohesive force so 

 essential in building up the woody axis has been considerably spent. In the 

 purely pistillate forms we almost always observe an unusual axial activity. 

 The female flowers in the regular forms are sessile in the axils of the leaves ; 

 but in the mostly pistillate forms they are generally elevated on short pedun- 

 cles, giving the plants a peculiar twiggy appearance. On the other hand, the 

 nearly male plants, which by the way are rarely seen, present characteristics 

 the reverse of these. The heads, usually female, wlien appearing as male 

 flowers, exist as large burrs tightly set in the axils, without the slightest ten- 

 dency to pedunculation. Though varying in intensity, and occasionally inter- 

 mingling, no one can fail to see that these forces prevail in these forms — the 

 feminine, in connection with cohesive and vital activity in the axillary parts 

 — the masculine, with weakened axillary activity, and individualization. 



The flowers themselves, however, afford a better illustration of this than the 



1869.] 



