96 INTRODUCTION 
this. These will be thoroughly described later on (cf. also p. 67). In this place 
the various forms of nectary will not be fully considered, but one example may serve 
to indicate in what variety these organs may occur even within a single family, 
the Ranunculaceae (Fig. 12). 
The form of the nectaries is not always the same, even in one and the same 
species of plant. Herm. Miiller gives in his works two particularly striking examples 
of the kind, i.e. Ranunculus auricomus (‘ Fertilisation,’ p. 79) and R. pyrenaeus 
(‘ Alpenblumen,’ p. 133) (see Fig. 13). 
Fic. 13. (1-8) Different petals of Raszunculus auricomus with diversely-formed nectaries (7). 
(9) Petal of Zranthis hyemalis. (After Herm. Miiller.) 
Nectar-covers, which also were frequently mentioned by Sprengel, and which are 
formed by projecting parts of flowers, processes, hairs, and so forth, serve as a means 
of protecting nectar from rain. Owing to such shelter nectar is not only saved from 
dilution, or even from being washed away, but more abundant secretion and 
accumulation are also rendered possible, with the result that insect visits are more 
numerous. On the other hand, since the nectar is sheltered deeper down, numerous 
of the less industrious insects are debarred from visiting and pollinating the flowers. 
In order to render more easy the finding of nectar by insects that have been 
attracted by colour or odour there are, as Sprengel pointed out (see pp. 4-6), many 
spots or lines on the flower, which by their position or direction indicate the place 
where the honey is concealed (cf. Fig. 14). These Nectar-guides, however, are 
naturally only present in such flowers as are visited by insects during the day. They 
are wanting (see p. ob in moth flowers, nner they would be useless (cf. also 
Sprengel, ‘ Entd. Geh.,’ p. 16). 
The Pesior sudo of one and the same species of plant have not always the 
same form, but may be developed in various ways. I have described (‘ Bl. u. Ins. a. d. 
Nordfries. Ins.,’ p. 52) and figured (see Fig. 15) such variable nectar-guides in 
Erodium Cicutarium. 
The correctness of Sprengel’s theory of nectar-guides has often been doubted ; 
but it may be accepted as valid till some other and better explanation can be given of 
the dots, lines, streaks, and markings that occur on the petals of flowers. 
In support of Sprengel’s theory of nectar-guides Hildebrand mentions (‘Die 
Farben der Bliiten,’ p. 72) a phenomenon frequently exemplified by double flowers. 
It appears that when nectar-guides are strikingly developed in the simple form of 
