494 ^^^ NEROGA MS. 



of leaves, but the preceding whorl of carpellary leaves swell up after fertilisation, and 

 envelope the seeds in a pulpy mass, the berry-like fruit of these plants. In Primulaceae 

 the ovules spring from the elongated floral axis itself, and thus correspond in their 

 position to entire leaves ; they are however enclosed, even at the period of their 

 formation, by an ovary, consisting of the carpels and an elongated style bearing the 

 stigma. In most other Dicotyledons and Monocotyledons the ovules are seated on 

 the revolute margins of the carpels which have grown together into an ovary, and 

 which therefore in these cases both produce and enclose the ovules. But notwithstanding 

 these very considerable morphological differences, the carpellary leaves are always alike 

 physiologically in being excited by fertilisation to further development during the 

 maturing of the seeds, and in taking a certain share in their future history. 



Pollination and Fertilisation. By Pollination is meant the conveyance of the pollen 

 from the anthers to the stigma of Angiosperms or to the nucellus of Gymnosperms. 

 The pollen is detained there by a viscid substance, or often by hairs, and the emission is 

 thus brought about of the pollen-tube which in Gymnosperms penetrates at once the 

 tissue of the nucellus, but in Angiosperms grows downwards through the tissue of the 

 stigma and the frequently very long style in order to reach the ovules ; it then forces 

 itself into the micropyle and advances as far as the embryo-sac. It is only when it 

 reaches the embryo-sac (in Gymnosperms however it penetrates still more deeply) that 

 fertilisation of the oosphere results. A considerable time, occasionally even months, 

 often elapses, between pollination and fertilisation ; but commonly only a few days 

 or hours. 



Pollination is rarely effected by the wind alone, those plants in which this is the case 

 are said to be anemophilous ; in this case large quantities of pollen are produced in order 

 to secure the result, as in many Goniferae. In a few cases the pollen is thrown on to the 

 stigma by the bursting of the anthers (e.g. in some Urticaceae) ; but the means usually 

 employed is that of insects, and the plants in which this is the case are said to be 

 entomophilous. For this purpose special and often very complicated contrivances are met 

 with to allure insects and attract them to visit the flowers ; and at the same time the 

 object is accomplished of always conveying, where possible, the pollen to the stigma of 

 a different flower to that which produced it (even when they are hermaphrodite). 

 In reference to this object the parts of the flower also assume definite forms and 

 positions, which will be followed out further in Book III. Here it need only be 

 mentioned that insects are especially attracted to visit flowers by the nectar 

 secreted in them ; this usually sweet juice is generally produced deep down among 

 the foliar structures of the -flower, and the form of the parts is generally so contrived 

 that the insect, while it is obtaining the nectar, must place its body in certain definite 

 positions by which it at one time brushes the pollen out of the anthers, at another time 

 attaches it to the stigma of another flower. The diversity in the forms of flowers 

 depends especially on these relationships, a comparatively simple plan of structure 

 underlying them all. The organs which secrete the nectar, the Nectaries, are 

 therefore of extreme importance in the life-history of most Phanerogams; they are, 

 nevertheless, usually very inconspicuous, and, — which is very significant with respect to 

 the relationship of morphology with physiology,— notwithstanding their enormous 

 physiological importance, they are attached to no definite part of the flower in a 

 morphological sense ; almost every part is able to perform the function of a nectary. 

 This term therefore does not denote a morphological but a purely physiological idea. 

 The nectary is usually only a small spot at the base of the carpels (as in Nicotiana), or of 

 the stamens (as in Rheum), or of the petals {e.g. Fritillaria) which, without becoming 

 more prominent, produces the nectar; but frequently it is in the form of glandular 

 protuberances of the floral axis between the insertion of the stamens and petals (as 

 in Cruciferae and Fumariaceae). A particular organ, e.g. a petal, is often transformed, 

 for the purpose of secreting and storing up the nectar, into a hollow receptacle, forming 

 a spur-like protuberance {e.g. Viola) ; or all the perianth-leaves become developed into 



