THE CROSSING OF FLOWERS. 301 



the stigma of another which contains the female sexual cells in its ovary; and we 

 may distinguish between crossing in plants of the same and of different species. 

 In the former case the pollen of one flower is deposited on the stigma of another 

 flower belonging to a plant of the same species ; in the latter case the pollen is 

 deposited on the stigma of a flower which is not of the same species. Obviously 

 in the latter process, which is also termed hybridization, the two flowers are some 

 distance apart. Of the former process there are two varieties, viz. Oeitonogam^y 

 (from yeLrwv, a neighbour, and 701^0$, marriage), when the two flowers are immediate 

 neighbours, growing upon the same plant, and Xenogamy (from ^^vos, a stranger, 

 and ydfios, marriage), when they are on different plants of the same species. 



Although the distribution of the sexes on different plants or in different 

 flowers of the same plant has been indicated as advantageous, even as a condition 

 for the occurrence of cross-fertilization, it must not be supposed that it is the 

 only contrivance for ensuring hybridization, xenogamy, or geitonogamy. It is 

 beyond question that the same result is obtained in true hermaphrodite flowers, 

 i.e. that plants whose flowers all contain fertile pollen-grains and ovaries which 

 are capable of development can cross with one another. Of course special arrange- 

 ments are necessary for this, and the more important of them will be mentioned 

 in the following pages and illustrated by a few examples. In some instances 

 cross- fertilization is unavoidable from the mutual arrangement and position of the 

 two kinds of sexual organs which occur together in a true hermaphrodite flower. 

 If during the whole time of flowering the stigma assumes such a position as to 

 be brushed by an insect which is visiting the flower, but at the same time is so 

 placed that it cannot receive the pollen from the anthers immediately surrounding- 

 it, it may be safely assumed that it is adapted to cross-fertilization. This is 

 the case, for example, in the White Lily {Lilium album), Day Lily (Hemerocallis 

 flava and fulva), AntJiericum, and numerous bulbous plants of the Cape (Amaryllis, 

 Albuca, &c.) The entrance to these flowers is directed laterally, and the style 

 projects so far beyond the anthers with their sticky pollen that its stigma never 

 receives any of it. On the other hand, when the projecting style is used as a 

 resting-place by flying animals which come laden with pollen from another flower, 

 it is unavoidable that foreign pollen should be deposited on the stigma, and so 

 a crossing results. The same is true of various Boraginacese (e.g. Echium), Scro- 

 phulariacese (e.g. Pwderota Ageria), Bindweeds (e.g. Convolvulus sepium, syl- 

 vaticus, lucanus), Caprifoliacese (e.g. Linnma borealis). Rhododendrons (e.g. Eho- 

 dodend.ron Chaoncecistus), and Cactaceee (e.g. Mamillaria, Echinocactus). Many 

 flowers whose entrance is directed upwards (e.g. Lilium. bulbiferuTYi, Glaucium 

 hbteum, Gentiana Bavarica, nivalis, verna) show the same condition of anthers 

 and stigmas. In the flowers of the Mezereon {Daphne Mezereum) the stigma is 

 not beyond and above the anthers, as in the plants just mentioned, but it forms 

 the termination of the ovary at the base of the perianth-tube, whilst the anthers 

 are situated in the upper part of the tube. Some pollen may occasionally fall 

 from the anthers on to the stigmas in erect flowers, especially when they shrivel 



