August 17, 1882] 



NATURE 



373 



grass-plant. It is impossible, however, to examine the 

 functionless corolla without coming to the conclusion that 

 Plantago must be descended from an entomophilous an- 

 cestor. Indeed, P. media still to some extent lays itself 

 out to attract small flies, by which it is even now often 

 visited and fertilised. 



The Rosacea offer some good examples of green flowers 

 in which the petals have become quite extinct. Some of 

 them are entomophilous, and some anemophilous. Alche- 

 milla vulgaris (lady's mantle) is one of the former class. 

 It is a degraded representative of the same group as 

 agrimony ; but it has lost its petals altogether. That it 

 is a late, not a primitive form, is shown by its very re- 





Fie. 35. Fie. 36. Fie. 37- 



Fig. 35— It-male ilower of willow, 'reduced to a scale and an ovary. Fig. 

 36. — Male flower of willow, reduced to a scale and two stamens. Fig. 37. 

 — Naked flowers of the Arum, each consisting of a single ovary or a few 

 1 aked .stamens. 



duced carpels, and its small number of stamens. Alche- 

 milia arvensis (parsley-piert) is an extremely debased 

 moss-like descendant of some similar ancestor. It has 

 tiny green petalless axillary flowers, self-fertilised, but 

 occasionally visited by minute insects. Not far from these 

 may be placed Poterium sanguisorba (Fig. 27), another 

 degraded type, which has become anemophilous. This 

 flower, too, is green, and has no petals ; it usually pos- 

 sesses but one carpel, and it is altogether a clearly 

 debased bisexual form. Its stamens are numerous, and 

 they hang out to the wind, so do also the feathery stigmas 

 in the female flowers, to catch the pollen from neighbouring 

 heads. But the closely-allied Sanguisorba officinalis (Fig. 

 28) is evidently an entomophilous variation on the same 



Fie. 38— Single fl 



rof Acort/s, with three sepals, thr< 

 and an ovary. 



petals, six stamens. 



ancestral form ; for it resembles Poterium in every respect 

 except in its flowers, which have very few stamens, in- 

 closed in the purple calyx-tube. This interesting case 

 shows us that when a flower has once lost its petals and 

 become anemophilous, it cannot re-develop them if it 

 reverts to insect fertilisation, but must acquire a coloured 

 calyx instead. The same lesson is perhaps elsewhere 

 enforced by Glaux maritima among the PrimulacecB, and 

 by Clematis among the Ranunculacea. 



Mr. Darwin remarks that anemophilous flowers never 

 possess a gaily-coloured corolla. The reason is clear. 

 Such an adjunct could only result in the attraction of 

 stray insects, which would uselessly eat up the pollen, 



and so do harm to the plant. Hence, when flowers rever 

 to wind-fertilisation, both disuse and natural selection 

 cause them to lose their petals, and become simply 

 green. 



In practice, however, it is often hard to distinguish 

 between the casually entomophilous, the self- fertilised, and 

 the. really anemophilous species ; and they are so inter- 

 mixed that it may perhaps be best to consider them 

 together. For example, the common ash (Fraxinus 

 excelsior) belongs to a gamopetalous family, the Olcacece, 



Fig. 39. 

 Fig. 39— Fbwer of Scir/rt 

 the calyx and corolla, 

 showing two lodicules c 

 with two stigmas. 



', a sedge, with hypogynous bristles representing 

 Flo. 40. — Flower of a grass, with calyx removed, 

 ■rudimentary petals, three stamens, and an vary 



and is closely related to the white privet {Ligustrum 

 vu/gare), which has conspicuous white flowers. But 

 many large trees, owing, perhaps, to their long life, and 

 consequent less necessity for producing many seeds, tend 

 to lose their petals ; and this is remarkably the case 

 among the olive group. The shrubby species have 

 usually flowers with a four-lobed corolla ; and so have 

 many of the southern arboreal forms (Fig. 29); but the 

 northern trees, like our ash, have lost both calyx and 

 corolla altogether, each naked flower consisting only of 



cu. 



Fig. 41. — Diagram of grass flower, showing its relation to a lily : a. the 

 calyx, represented by <z It the flowering glume or outer palea, and .r, and 

 03, the inner palea. c nipnsed of two connate sepals; £, the c r .lla, 

 represented by />, and b^, the lodicules, />$ the third petal, being obsolete ; 

 r, the stamens ; ,/, the" pistil, d, and i/ 2 [he existing stigmas, rf 3 being 

 obsolete. The whole flower is thus abortively developed on the inner 



,.,:.. 



the: 



two stamens, with a single ovary between them (Fig. 30). 

 In appearance their blossoms seem of much the same 

 sort as the wind-fertilised catkins and oak-kinds. Never- 

 theless, they are entomophilous, for their pollen, their 

 arrangement in large masses, and their dark purple colour, 

 sufficiently serve to entice numerous insects. 



The spurges (EuphorbiaeeoS) are a very interesting 

 family of the same sort, exhibiting every gradation from 

 perfect corolliferous blossoms to the most degraded 

 flowers in all nature. Our English species have no true 

 petals ; but some exotic forms are truly dichlamydeous ; 



