272 NATURAL SCIENCE. April, 



from afar, by showing the presence of honey, the insects that are 

 swarming about in the air in search of food. 



" Examining, in the summer of 1789, some species of Iris, I soon 

 found that Linnaeus had erred in regard both to the stigma and the 

 nectary ; that the honey is fully protected from rain ; and, finally, 

 that there is a specially coloured place, leading insects to the honey. 

 But I found more than this, namely, that these flowers cannot be 

 fertilised at all except by insects, and then only by insects of fairly 

 large size. Although I did not, at the time, find this idea confirmed 

 by experience (this occurred in the following summer, when I actually 

 saw humble-bees creeping into the flower), still I was convinced of 

 its truth by the general appearance. I endeavoured, therefore, to 

 discover whether other flowers are also so constructed that they can 

 only be fertilised by insect agenc3\ My investigations convinced me 

 more and more that many — perhaps all — flowers which contain honey 

 are fertilised by insects which feed upon the honey, and that, conse- 

 quently, this nourishment of the insects is, in regard to them, the 

 final end, but, in regard to the flowers, is only a means, and, indeed, 

 the sole means, to a definite end, viz., their fertilisation, and that the 

 entire structure of such flowers can be explained, if, in their investi- 

 gation, one keep always in view the following principles : — 



" I. These flowers are fertilised by this or that species of insect, 

 or by several. 



"2. This also will occur, that the insects, as they visit the 

 flowers for honey, and in consequence of this, either rest upon the 

 flowers in some indefinite way, or in a definite manner either creep 

 into the flowers or run round upon them, will, of necessity, be smeared 

 with pollen from the anthers, either over the greater part of their 

 hairy bodies, or only over a part of them, and will rub this pollen 

 upon the stigma, which, for this end, is either covered with short and 

 fine hairs, or with a damp, often sticky, secretion. 



" In the spring of 1790 I perceived that Orchis latifolia and O. Morio 

 have, in all respects, the structure of a honey flower, but do not con- 

 tain honey. I thought at first that this observation, if it did not 

 actually overthrow my former discoveries, would at least make them 

 very doubtful. For, since these flowers have a honey guide (so have 

 I termed the differently coloured spot on the corolla) — and yet this 

 cannot show insects the road to the honey, as there is none - — it 

 appeared to follow that the honey guides also, on those flowers which 

 do contain honey, were not really for this purpose at all, and that the 

 whole thing was a mere fancy. I must, therefore, confess that this 

 discovery was in no way pleasant to me. But just this spurred me 

 on to study these flowers more attentively, and to observe them in 

 the field, and at last I discovered that these flowers are fertilised by 



- Darwin showed that insects visiting Orchis drill holes into the tissue of the 

 spur and suck the juice therein contained, so that the flower is not really an exception 

 to Sprengel's views. 



