PHANEROGAMS. ^20 



of the ovule, and when this latter becomes developed in a leaf-like manner it appears as 

 an outgrowth of the surface of the leaf. This fact, the morphological importance of 

 which was first insisted on by Cramer, is however not universal, as is especially shown 

 in the development of the ovules of Orchideae, the nucleus of which unquestionably cor- 

 responds to the apex of the entire ovule, although it becomes anatropous by subsequent 

 curvature ; still less possible does it appear to consider the nucleus of the orthotropous 

 ovule of Taxus and Polygonaceae as a lateral formation, since it is obviously an elongation 

 of the apex of the floral axis (see Angiosperms). 



The Carpellary Lea'ves are the foliar structures of the flower which stand in the 

 closest genetic and functional relationship to the ovules. They either produce and 

 bear the ovules, or are constructed so as to enclose them in a chamber, the O'vary, and 

 to form the apparatus for the reception of the pollen, or Stigma. The distinct morpho- 

 logical significance of the carpellary leaves is clearly seen by a comparison of the genera 

 Cycas and Juniperus. In Cycas the carpels resemble the ordinary leaves of the plant, 

 and the ovules are produced on their margins and remain entirely exposed ; in Juniperus 

 the ovules spring from the floral axis itself, corresponding, even in their position, to a 

 w'horl 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 

 Primulaceai 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 diflerences, 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. 



Pollhiation and Fertilisation. The mutual action on one another of the pollen and 

 the embryonic vesicle of Phanerogams, the latter already formed in the embryo-sac, 

 results in two phenomena of extreme importance, to be carefully distinguished from one 

 another: Pollination and Fertilisation. By Pollination is meant the conveyance of the 

 pollen from the anthers to the stigma of Angiosperms or to the nucleus of Gymno- 

 sperms. 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 nucleus, 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 embryonic vesicle results. A considerable time, occa- 

 sionally even months, often elapses between pollination and fertilisation ; but commonly 

 only a few days or hours. 



Pollination is rarely effected by the wind alone; in this case large quantities of 

 pollen are produced in order to secure the result, as in many Coniferse ; in a few cases 

 the pollen is thrown on to the stigma by the bursting of the anthers {e.g. in some Urti- 

 caceae) ; but the means usually employed is that of insects. 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 



