FLOWERING-PLANTS. 757 



is not one of principle but only of degree. That which conspicuously distingtiis hes 

 particularly the large and elegant flowers of true flowering-plants from those of .t he 

 Symnosperms is the floral envelope, which is very often a dnuhle nn^ gn f^ ia- thpn 

 t^rmsd Calyy anrl CInrnlla. F.vpn thp most magnificent flowers when stripped of these 

 envelopes so that only the essential organs of reproduction remain, show nothing 

 more of the immense contrast indicated above, and we have here to do particularly 

 with these proper reproductive organs only, although I shall show in the next lecture 

 that the floral envelopes are by no means superfluous for starting the process of 

 fertilisation (i. e. pollination), and in many cases are in fact indispensable. 



In considering the fertilising apparatus of a flower, as I now have it in mind, 

 it is above all evident that both kinds of reproductive organs, the male and female, 

 are very generally united in one flower, and therefore stand next one another close 

 to its growing-point ; or, in other words, most flowers are hermaphrodite, whereas the 

 floral structures of all Gymnosperms always contain only male or only female organs, 

 both kinds of flowers being distributed on the same tree or on different trees of 

 the same species. These two cases of diclinous flower-development are it is true by 

 no means rare even in flowering-plants, the Monocotyledons and Dicotyledons, plants 

 of the Cucurbitaceae for example having male and female flowers on the same 

 foliage-shoot, whereas the Hemp or Hop bears always only male or only female 

 flowers on a plant. The prevailing rule however is that the flowers are hermaphro- 

 dite — a fact which is of importance physiologically, because a long series of the 

 most remarkable mechanisms for pollination are entailed by it, to which I 

 shall have to refer later. Also the two kinds of fertilising organs, as such, are very 

 different from those of the Gymnosperms. Whereas the male spores or pollen- 

 grains of the Gymnosperms arise in receptacles which obviously agree with the 

 sporangia of Cryptogams, and particularly in that they are developed on leaves 

 which are often only slightly different from ordinary foliage leaves ; we find on the 

 contrary that the male fertilising organs of the true flowering-plants, the stamens, 

 usually have forms which do not easily disclose their true morphological nature. 

 Very generally a stamen consists of a stalk-like support (the filament) which bears 

 above the so-called Anther; this again consists chiefly of four sacs joined in two 

 pairs, or occasionally of only two sacs, in which the pollen-grains or microspores 

 arise. These sacs are to be regarded as the same as the sporangia, especially 

 the microsporangia of the Cryptogams and Gymnosperms ; but it is shown only after 

 further examinaion and consideration that the filament and the portion (connective) 

 connecting the pollen-sacs of an anther are together to be regarded as a metamor- 

 phosed leaf. 



Still more important than these peculiarities of the male fertilising organs, is 

 the structure of the female organ. Here we meet with a profound difference between 

 the true flowering-plants and the Gymnosperms. In these latter the ovules arise at 

 the margins or on the surfaces of foliar organs, and this so that they are either 

 freely exposed, as in Cycas revoluta and Gingko biloba, or else so that they 

 are simply concealed between the closely packed leaves : at least the micropyle of 

 all Gymnosperms is in open communication with the atmosphere at the time of 

 pollination. Nevertheless in most Coniferae the pollinated ovules usually become so 

 completely enclosed in enveloping leaves subsequently, that all ommunication with the 



