238 



NATURE 



\yan. II, 1877 



logico-Botanical Society in Vienna. The following is a 

 brief outline of this paper :— 



M. Kerner, first of all, thinks it unwarrantable to divide 

 the characters found in plants into physiological, which 

 bring- their possessors a certain advantapfe, and morpho- 

 logical, which are of no advantage. While, no doubt, 

 profitless and even disadvantageous formations occur in 

 plants, it is yet certain that such individuals are soon 

 extinguished and suppressed by others which bear advan- 

 tageous characters. Most of the so-called morphological 

 characters have rather a certain biological significance, 

 and it is only from the lack of observations regarding 

 them that the material for their comprehension is so 

 defective. 



Hitherto study has mostly been directed to the relations 

 between the forms of flowers and those of the animals 

 visiting them. M. Kerner gives an account of those 

 manifold forms hitherto regarded as only of morphological 

 significance, but the use of which is to guard flowers 

 against uninvited guests and against all injurious influ- 

 ence, and attacks to which they may be exposed ; these 

 forms therefore are of essential biological value. 



How numerous are these enemies and uninvited guests 

 will appear from the following brief sketch : — First, there 

 are the large grazing animals, such as the ruminants, 

 solipedia, &c. Then there are snails, especially the 

 voracious Helicidse, which, indeed, are seldom found 

 in the flowers, not because they despise them, but 

 because they are kept from them by a group of stiflf 

 bristles and prickles underneath the flowers. The same 

 holds for soft insects, especially many larvae of cater- 

 pillars. The wingless aphides are, specially among soft 

 insects, to be noted as unwelcome guests of flowers. 

 They are found extremely seldom in flowers, being warded 

 off by suitable means, but if they are carried into the 

 flower they immediately force their proboscis into the 

 sappy tissue. The insects with a firm chitinous skeleton, 

 again, easily pass over the bristles and prickles ; only 

 their posterior feelers are sensitive to contact with sharp 

 points. Among animals of this class those are injurious 

 to flowers which, in consequence of their too small size 

 do not, in passing through to the nectar at the bottom of 

 the flower, brush against either the anthers or the stigma. 

 They take away the nectar without effecting fertilisation. 

 But even when the chitinous insects are of the proper 

 size they are unwelcome to flowers if they are wingless, 

 for in that case they are a comparatively long time in 

 reaching the flower of another individual of the same 

 species, and the pollen with which they are laden is 

 exposed to so many hazards, that fertilisation by these 

 insects is extremely improbable. 



Now the means of protection against access of these 

 numerous animals are very various, as we shall pre- 

 sently see. 



We may first notice the protection afforded by the 

 leaves, which produce the buildmg materials of the flowers 

 and are necessary to their growth. They aff"ord protec- 

 tion through certain alkaloids and other compounds con- 

 tained in the cell-gap, and also through a hard leather-Hke 

 consistence and thorny processes by which a portion of 

 the leaves are protected from injury by grazing animals. 



The means of protection in the flowers consist, first of 

 all, in the production of matters which are repugnant to 

 some animals ; such are alcohols, resins, and etheric oils, 

 to which a number of the unwelcome guests have such a 

 dislike that they will rather endure the sharpest hunger 

 than eat these plants. 



A second kind of protection consists in prevention of 

 approach to the flowers by isolation of these with water, as 

 is the case in the Bromeliaceae. Generally the foliage 

 leaves have funnel-like forms in which the atmospheric 

 precipitates, rain and dew collect and so form an in- 

 surmountable barrier to the passage df creeping, wing- 

 less insects, while the access of the flying insects which 



affect fertilisation is not prevented. The water-plants are 

 also defended against unwelcome guests which might 

 otherwise creep to them ; and it is very remarkable that 

 in water plants with projecting flowers, other means of 

 protection against creeping animals are wanting ; they 

 are only developed when the isolating layer of water, from 

 some cause or other, disappears. Very instructive in this 

 relation is the behaviour of Polygomim amphibiiim. To 

 the flowers of the plants growing in water, creeping 

 insects cannot come, the flowers being surrounded with 

 water. When, however, the water has run off and the 

 plant is on dry ground, there develop on the leaves and 

 stalks gland-hairs, which secrete a sticky matter, render- 

 ing the flower-bearing axis all smeary, so that access 

 is equally forbidden to the creeping insects. If, now, a 

 plant of Polygonum bearing these gland-hairs be put in 

 the water again, the trichome-tufts with their sticky mate- 

 rial disappear, and the surface appears once more smooth 

 and even. 



Such a formation of sticky matters is developed in 

 very many plants as a sure protection against unwelcome 

 visitants. These sticky matters appear on the most dif- 

 ferent parts of plants, under the flower, and ward off 

 especially creeping, but also unwelcome flying animals 

 from the flowers. The variety of the glandular forms 

 yielding sticky matter is very great, and their occurrence 

 is very widespread. 



While these sticky matters are effective against creep- 

 ing animals which have a pretty firm chitinous coat, and 

 especially against ants, they are ineffective against the 

 soft creeping animals, e.g., the snails, which secrete slime 

 on the sticky parts of the plants, enabling them to pass 

 over these. Against such enemies the plants are armed 

 with the most various thorns, prickles, and sharp teeth, 

 which mostly have their points directed downwards, but 

 may have the most diverse positions and forms. Quite 

 peculiarly interesting are those prickles and needles, 

 which serve the purpose not so much of keeping off 

 unwelcome visitants as of showing to the insects which 

 visit the flowers the right way for effecting fertilisation ; 

 whereas if the same insects visited the plants and re- 

 moved the nectar by another way, fertilisation would not 

 be accomplished. 



The means of protection thus far described are all on the 

 path which the unwelcome guest must traverse if he would 

 reach the flower. There are other means of defence, how- 

 ever, within the flower itself. These, indeed, cannot be re- 

 garded as absolute, for they may be overcome by unwel- 

 come visitors. They consist of hair-like formations, 

 which are united in large numbers, into grating-like 

 groups, rendering access impossible to one animal, 

 while to another, which is furnished with a longer, thin 

 proboscis, or can drive with greater force against the 

 grating, they yield the desired food. These soft hair 

 formations, which have the most various modifications 

 towards the end in question, also often serve to point the 

 way by which welcome visitors may reach the nectar. 



Where all the formations that have been mentioned are 

 wanting, protection is still afforded by bends, enlarge- 

 ments, and collocations of particular parts of plants, which 

 are so diverse that it is difficult to indicate them cursorily. 

 In general they may be divided into two groups, one of 

 which comprises those formations by which the nectar is 

 completely covered, whereas in the other the entrance is 

 merely narrowed so that an opening remains by which the 

 animals may introduce their sucking organs. The most 

 different parts of the flower share in these formations, pro- 

 ducing a very great variety of forms. 



A last means of protection of flowers is represented in 

 those numerous cases in which the flowers open only in the 

 evening, and thereby are guarded against the visit of in- 

 sects which swarm during the day. Further, there is the 

 diversion of injurious insects, due to the fact of the nec- 

 taries being sometimes situated in other parts of the 



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