

FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 401 



with the paucity of insects. Loew is of the opinion that the insects there are 

 adequate for the work they have to do, i.e. are sufficiently numerous for the main- 

 tenance of the species of plants which depend upon their visits. 



Putting aside the visits, and proceeding to consider the climatic conditions, w^e 

 are on much surer ground. Both on the mountains and in the far north the period 

 of vegetation is a short one, and the shortness of the summer, combined with the 

 broken character of the weather, which is common to the Alps and Arctic regions 

 during that period, can hardly fail to promote autogamy amongst the plants grow- 

 ing in those regions. Such as have flowers that can pollinate themselves spontane- 

 ously will be more sure of ripening their seeds before the brief summer ends than 

 will such the flowers of which must wait for insects. In the foregoing pages 

 several instances have been described in which autogamy is promoted by the closing 

 of the flowers. By these movements the pollen is mechanically transferred to the 

 stigmas. It may well be that by the considerable increase which must accrue in 

 these closing movements, owing to the frequency of unfavourable weather in alpine 

 and arctic regions, a further condition favouring autogamy is obtained. 



FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 



Pollination, or the dusting of the stigma with pollen, is only the prelude to 

 the phenomenon known as Fertilization. It is important to distinguish clearly 

 between these two events, especially as the term "fertilization" is frequently used 

 by authors when they really mean "pollination" — indeed, this substitution is almost 

 inevitable in many cases, the custom being what it is. Fertilization can only occur 

 in Phanerogams after previous pollination, though pollination does not invariably 

 connote a subsequent fertilization. Thus, cases are known in which flowers, polli- 

 nated by insects at the proper time, do not produce fruit, and others in which the 

 pollen of the same flower falls upon the stigmas with a like failure of result. In 

 other words, both cross-pollination and autogamy may be without result. 



It must be explained, to prevent misunderstanding, that the older accounts of 

 this lack of result attending pollination should be received wnth caution. Formerly, 

 judgment was passed rather hastily as to the results of pollination in hermaphro- 

 dite flowers, as it seemed obvious that the sexual elements must, unavoidably, come 

 I together. If no production of fruit took place in a really hermaphrodite flower, it 

 i was assumed that pollination was without result, and no precautions were taken to 

 j demonstrate that pollination had actually occurred. Thus it happened that certain 

 I plants were regarded as sterile, although this sterility had only been observed upon 

 ' isolated specimens growing in gardens. In many cases the flowers of the plants in 

 question were strongly protogynous, i.e. at the time when the stigmas should have 

 , been pollinated there was no pollen, there being no plants growing near with 

 ' flowers in a more advanced stage. Similarly, such flowers cannot be autogamous, 

 as the two sets of organs are never at maturity simultaneously. They are marked 

 out for cross-pollination. When for any reason this does not take place, fertilization 



I 



