JtNE, 1901. 



KNOWLEDGE. 



127 



I loii on tlic plant s part betwoen >uital)K- and un>uitalilo 

 insects: a fcatnr,; which becomes loniaikablv dcvelojied 

 m many of the more higlily specialized tlowcrs. Tlicv 

 cannot afford to give honey and to dust pollen on every 

 vl^ltor ; and along with an-angcnient.s made to suit 

 welcome insects may be found <mi equally elalwratc series 

 of precautions against the visits of insects which do 

 not assist fertilization. Crawling animals constitute 

 a large proportion of these unwelcome guests, for in the 

 tedious journey downi the st«m, perhaps across rough 

 ground, ajid up a neighbouring st«ni. whatever jjollcn 

 had adhered to the body, say of an ant, would inevitably 

 be wiped off before the insect reached another Hower. 

 Such useless visitors are kept away from flowers by 

 various devices — by palisad?s of downward-pointing 

 bristles, and entanglements of hairs or down, on the 

 stems or on the calyx ; by quagmires of gummy excre- 

 tion ; sometimes even by means of a moat full of water, 

 a-s in the case of the Teasel. How effective these baniers 

 are a little observation will show. Prof. Kerner counted 

 small animals of sixty different kinds — beetles, flies, ants, 

 bugs, ichneumons — trapped by the sticky stems of 

 ,'<ilfiie riiiftiii^ in the Tirol ; and the viscid hairy stem 

 and calyx of a Moss-rose must prove a practically im- 

 passable barrier to would-be explorers. Often the pro- 

 tective appliances are found in the blossom themselves, 

 and this brings us back to some of the irregular flowers 

 which we were considering. The Snapdragons and Toad- 

 flaxes exhibit a simple and complete method of protection 

 from small prowlers. The flower is shaped like a mouth, 

 with two closed lips ; the pollen and honey are in the 

 interior cavity. It is only an insect which is strong 

 enough to force open the lips, or whose weight, depend- 

 ing from the lower lip. is sufficient to depress it, which 

 can reach the interior of the flower. In other cases 

 the stamens form a ring which must be pushed aside 

 before the honey is reached. The encouragement of 

 useful insects and the discouragement of useless ones, 

 go baud in hand. 



The Salvias furnish a pretty case of exact adjust- 

 ment for their insect visitors. The flowers are exceed- 

 ingly irregulai", the upper part of the corolla forming a 

 high arch over the flower, the lower part forming a 

 broad landing-place for the insects. The corolla is pro- 

 longed downwards into a narrow tube, at the extremity 

 of which is the honey-well. The stamens and ■■style, as 

 the stalk of the stigma is called, curve along the arched 

 roof of the flower, above the entrance. The stamens are 

 hinged near the end, the free portion being prolonged 

 downwards, and hanging in the entrance. When an 

 insect alights on the platform, and inserts it^ head into 

 the flower in order to di-aw honcv from the well, it 

 pushes the end of the hinged portion of the stamens 

 inward and upward, with the result that the opposite 

 end, which bears the pollen, swings downward and strikes 

 the hind portion of the insect's back. And there is a 

 further point. It has already been noted that most 

 flowers, in order to produce pei-fect seed, should be 

 fertilized not with their own pollen, but with the pollen 

 of another flower of the same species. In the Salvias 

 the stamens are ripe and shed their pollen before the 

 stigma is in a receptive condition, and in this way (as 

 in a great many other flowers) self-fertilization is avoided. 

 But the style continues to grow, and by the time the 

 stigma is mature it has outgrown the stamens, and 

 occupies exactly the position which the stamens occupied 

 on striking the insect's back. So that our insect, on 

 visiting a slightly older flower, brushes the stigma with 

 precisely that portion of its back on which the pollen 



was deposited. It is to be noted that a small insect, 

 visiting this flower, would not touch the stamens or 

 stigm.i. under which it would walk to the honey-well, 

 which it would tind too narrow to allow of its entrance, 

 and too deep to be sounded by its short proboscis. It 

 would go away, having (li^turlicd neither the pollen nor 

 the honey. 



It is in the Orchid tribe that specialization of this 

 kind has been carried furthest, and in these plants we 



Insec-t-fertilized flowers, elunviuj eou>picuous effect produced (1) 

 by great enliirgement of the corolla (Co«ro/t'«/Ki), and (2) by the 

 grouping in a larije umbel of numerous smaller llowers (Angelica). 



Phnlo.j.aph ',./ U. Welch. 



find an ingenuity of design, and a wealth and variety 

 of form and colour, that ai-e unequalled in the vegetable 

 kingdom. Some of the common Orchids of our meadows 

 will exemplify their structure quite as well as the most 

 gorgeous Brazilian species. Examine one of our common 

 British Orchids, .such as On-hix wnciihifn or HaliiiKiria 

 hifolia — they are just coming into bloom now. The 

 calyx consists of three sepals, the corolla of three petals ; 

 all are colour-id similarly, but dift'er in shape. It must 

 be pointed out that these flowers, when mature, are all 

 upside-down, as we may see by opening a bud, and com- 

 paring the relative positions of the parts with those 

 of an open flower. This inversion of the flower is 

 caused by a twisting of the ovary, or seed-vessel, which 

 is long, and looks like the stem of the flower: this 

 twisting also we may observe by comparing the ovaries 

 of a bud and of an open blossom. The large petal which, 

 in the bud, is topmost, and folds over the other portions 

 of the flower, in the open blossom is lowest, and forms 

 a broad landing-stage. Two sepals stand one on either 

 side ; two petals and the remaining sepal form the roof 

 of the flower. The lowest petal is prolonged backwards 



