DAEWIN ON PEBTILIZATION OF ORCHIDS. 373 



how varied are the accomplishments, how laborious the investigations, 

 and how sharpened become the faculties of a working naturalist with 

 a theory to establish, and how subservient the latter may always be 

 kept to the sternest demands of facts and their teachings. 



The book opens with a brief description of the structure of 

 Orchid flowers, and of the terms applied to their organs, and is divi- 

 sible into three parts, of which the first is devoted to British Orchids, 

 the second to exotic forms, and the third to general considerations on 

 the structure, morphology and physiology of Orchids. Such at least 

 would be our division of the work, but the author has disposed of 

 the whole matter in seven chapters, without concise headings, some- 

 what arbitrarily, as if the conception of putting forth the treatise as 

 a separate work were an after- thought ; an arrangement that does not 

 recommend itself to the general reader, who thus loses sight of the 

 grand divisions of the Order as well as of the subject. 



The general results obtained from all Orchids then are — 1. Tliat 

 the structural obstacles to self-fertilization are almost insuperable. 



2. That the adaptation of all parts of Orchid flowers is for cross impreg- 

 nation of one flower by the pollen of another of the same species o^^ 



3. That insects are the agents of fertilization almost invariaWy." 



4. That the labeUum is the landing place of the insects, and contains 

 the object of attraction to them in the shape of a honey-bearing spur, 

 or sweet pulpy excrescences, or nectar-distilling hairs. 5. That the 

 relative position of the labeUum to the reproductive organs is such, 

 that an insect to reach the attractive object in the former, places 

 head or thorax in contact with the latter. 6. That an insect on its 

 first visit to a hitherto unvisited flower, must in its search for honey 

 usually so place itself as to close the stigmatic cavity, while at the 

 same time it removes the pollen. 7. That in numerous cases, so 

 long as the insect remains on the plant whose flowers it has sucked, 

 the pollen retains such a direction as that it cannot reach the 

 stigma of any flower it visits ; and that, as owing to its unerring in- 

 stinct it never visits the same flower twice, it cannot reach the stigma 

 of that from which the pollen was taken. 8. That in many cases, after 

 a certain period, generally longer than that spent by the insect in one 

 flower or plant, the pollen spontaneously assumes such a direction 

 that it is infallibly applied by the insect to the stigma of another 

 flower of the same species as that from which it took the pollen. 

 Bearing these points in mind we shall now very briefly review the 

 principal modifications in structure and method of fertilization pre- 

 sented by the British genera of Orchids examined by Mr. Darwin. 



Orchis mascida, morio,fusca,maculata, latifolia, and Aceras anthro- 

 pophora. In these an insect alights on the labellum, and pushing its 

 head into the cavity at the base of the labellum, the rosteUum is 

 touched, its membranes ruptured along definite lines, and the viscid 

 balls at the base of the pollinia consequently cement themselves to 

 the insect's head or proboscis, with the poUinia erect. In this posi- 

 tion the pollinia cannot touch the stigma of a flower subsequently 



