September 2, 1895.] 



KNOWLEDGE. 



201 



is an inflorescence of the same description, not erect, how- 

 ever, but pendulous, and so flexible that it swings freely 

 in the lightest breeze. After the flowering period, the 

 ground under the oak, pojilar, and other trees, is strewn 

 with their male catkins ; these are caducous, falling off 

 soon after they have shed their pollen ; the catkins of 

 female flowers are necessarily persistent, though a few may 

 occasionally be broken off by the violence of the wind. 



In reeds and grasses the entire plant, being flexible, is 

 easily shaken by the wind, and the ripe pollen is readily 

 dislodged from the anthers : but where the stem is more 

 rigid either the flower-stalks are slender, or the stamens 

 have thin, thread-like filaments ; or the entire inflorescence 

 is mobile ; in any case provision is made in the structure of 

 the flower for the agitation of the anthers by the wind. 

 Slender flower stalks are seen in the dock and in the 

 quaking grass [BriaiJ. TJie ribwort plantain ( Plaiitmjo 

 linufoliitii I and a great many grasses have their anthers 

 borne on long, excessively thin stalks, so that they quiver 

 in the slightest breeze. Broad and leaf-shaped, the anther 

 itself in Plantago is clearly adapted, like the seed-vessels of 

 some crucifers, to be set in motion by the wind. On a 

 calm and warm day in summer the gentlest touch is 

 sufiicient to make many grasses, such as the foxtail, cock's- 

 foot or Timothy, emit a little 

 cloud of pollen. Some grasses 

 even appear to eject the pollen 

 with force either by the 

 explosion of the pollen-sacs 

 or by a sudden jerking of 

 the stamens. The nettle 

 and pellitory have each four 

 elastic stamens ; when the 

 flower opens, these are bent 

 inwards towards the centre 

 in a constrained position ; 

 later on, the tension is re- 

 moved and the liberated 

 stamens suddenly straighten 

 out, scattering their pollen 

 like little puffs of smoke. The object of this liliputian 

 artillery is to throw the pollen away quite clear of the 

 plant by which it was produced. 



Petals in ordinary flowers are intended to secure the 

 attention of insects ; to wind-fertilized blossoms, having 

 no occasion for visitors, they are unnecessary. So far 

 from an advantage, the presence of a corolla would exclude 

 the wind from the essential organs. Accordingly petals 

 are either absent altogether, or reduced to rudimentary 

 proportions. The calyx is also much reduced, and in some 

 flowers is dispensed with entirely. Comparatively few ane- 

 mophilous flowers possess both sets of floral envelopes. 

 Plantago is, however, dichlamydeous, but its chaffy petals 

 afford incontrovertible evidence of de- 

 generation from the entomophilous 

 condition. 



The stigma in the wind-fertilized class 

 is highly specialized, and much larger re- 

 latively to the other parts of the flower 

 than is the case with entomophilous blos- 

 soms. It is commonly penicillate, con- 

 sisting of a tuft of hairs as in the nettle ; 

 feathery, as in grasses ; or elongated and 

 threadhke,as in Plantago and the rushes. 

 The spirally twisted stigmas of the last- 

 mentioned flowers are beautiful objects 

 when examined with a pocket lens. The 

 larger the surface which the stigma pre- 

 sents to the wind, the greater are the chances of pol- 



FiG. 6. — Aueiiiophilons Flowers 

 A, Oat; B, Ari'owgrass. 



Fig. 7. — Dicbogamv 

 of the Ru-;li. 



lination. Its fine fringes of papillose hairs are also well 

 calculated to entangle the pollen-grains, while the viscid 

 secretion serves to retain them when caught. This 

 adaptation may be seen in the common rye grass ; 

 each tiny blossom as it expands hangs out its two white, 

 feathery stigmas from the sides of the spikelet, reminding 

 one of a fisherman spreading out his nets, or a sailor his 

 studding sails to catch the favouring breeze. At the time 

 of fertilization the dock, too, thrusts out its three little 

 brush-like stigmas between the lobes of the perianth. It is 

 instructive to compare these wind-fertilized flowers of 

 Rumex with those of the nearly allied genus Polygonum, 

 which is entomophilous. The perianth of the latter is 

 rose-coloured ; the stigmas are included within it, never 

 exserted as in the dock — they are not at all brush-like or 

 feathery, but in the form of little knobs ; the stamens and 

 flower-stalks are rigid ; moreover, the various species of 

 Polygonum secrete nectar and are frequented by many 

 different insects. Stigmas are entirely absent in the 

 gymnospermous division, but in most Coniferae the ovule 

 at the time of flowering secretes a drop of fluid, and the 

 pollen-grains caught on it are, as the fluid gradually 

 evaporates, stranded on the nucleus of the ovule. The 

 ovule of the larch is provided with elongated papillse, 

 functionally equivalent to a stigma. 



A flower is said to be hermaphrodite or monoolinous 

 when, as in the elm, both stamens and pistils are present 

 in the same blossom. With insect-fertilized flowers this 

 is mostly the case, though there are some exceptions, 

 such as the cucumber and begonia, which are unisexual 

 or diclinous, stamens and pistils being produced in separate 

 blossoms. The diclinous condition is exceedingly common 

 in the wind-fertilized class. The 

 staminate or male, and the pistil- 

 late or female flowers are some- 

 times found growing on the same 

 individual plant, which is then 

 termed montt-cious, as in the oak, 

 hazel, birch, pine, etc. The poplar, 

 willow, yew, juniper, nettle and 

 dog's-mercury, ou the other hand, 

 are dicpcious ; their staminate and 

 pistillate flowers grow on separate 

 plants. This separation of the 

 sexes renders self - fertilization 

 impossible, and secures whatever 



benefit may arise from the physiological division of 

 labour. Anemophilous species in general show a marked 

 tendency in the direction of separation. Self-fertilization 

 may be prevented in monoclinous flowers by the stamens 

 and stigmas maturing at different times. This arrange- 

 ment, known as dichogamy, occurs both in insect- and 

 wind-fertilized blossoms, but while the former usually 

 have the stamens in advance of the stigmas, in the latter 

 the reverse order is much more frequent. There are thus 

 two kinds of dichogamy — piotandrous, where the stamens 

 are in advance ; protogynous, if the pistils are first 

 developed. Protogyny is characteristic of wind-fertilized 

 flowers, and may easily be observed in the rush and 

 plantain. From the illustration it will be seen that, in 

 the first or female stage of the flower of the rush, the 

 thread-like stigma protrudes from the top of the still 

 unopened perianth, while the stamens, as yet immature, 

 are completely concealed. In the second stage the 

 pollinated stigmas have begun to shrivel, the perianth 

 has now spread out, disclosing the six stamens, which are 

 ready to discharge their pollen. The same two stages are 

 equally apparent in Plantago. All our readers must be 

 familiar with the black heads of this plant, which are to 



; 



Fig. 8. — Head 

 Plantago lanceolafa 

 two stages. 



