EXCRETION OF NECTAR. 28l 



extended in the substratum which absorb the water, and this is forced out again in 

 the form of drops on those parts which protrude above the substratum. Hence, how- 

 ever, it follows that the absorbing root-hyphse must offer more resistance to filtration 

 than the walls of the sporangium, and we have here at once a case which supports 

 my theory, adduced above, of the causes producing root-pressure. IMoreover other 

 Fungi, which consist of ordinary segmented hyphse, can also excrete water on 

 their fructification above the substratum ; this happens, for example, with the com- 

 monest of all mould-fungi, PenicilUum glauciwi. When it fruits, after forming 

 a dense membrane on the surface of a nutritive fluid, numerous drops of fluid 

 collect on the upper side of the fungus membrane. The Fungus Merulius lachry- 

 mans, which is found in cellars and is so exceedingly destructive, has evidently 

 obtained its name from a similar excretion of water. 



The drops of so-called nectar are also to be referred to the excretion of liquid 

 water. At the bottom of many flowers, at the base of the petals or stamens, or 

 more particularly on the cushion at the base of the flower, juices containing sugar 

 are excreted at the time of pollination, which are collected by bees and serve 

 for the formation of honey. These juices are distinguished in Botany as nectar. 

 Similar organs — i. e. nectaries — also occur however on other parts of plants, as on 

 the under side near the base of the lamina of Prunus lauro-cerasus, and right 

 and left on the petiole of Prunus avium, &c., also on the stipules of the common 

 field bean ( Vicia /aba). These nectaries excrete juices containing sugar when the 

 parts of the plant concerned are highly turgescent. The arrangements referred 

 to are especially conspicuous in the common Crown imperial {Fritillaria wiperialis), 

 where large, clear drops of nectar are excreted from rounded somewhat depressed 

 spots at the base of the petals; when these drops are shaken off", they become 

 replaced by others, and this even when the flower-shoot is cut off and placed in 

 water, whence it follows that in this case root-pressure is not needed, but rather 

 that masses of tissue exist in the neighbourhood of the nectary, from which the 

 water and its saccharine contents are excreted — a fact which is also to be observed 

 in other flowers. According to Wilson's researches, the renewal of the drops is 

 suppressed when the external surfaces of the nectary are washed with water; 

 they re-appear, however, if a very small particle of sugar is laid on the surface of 

 the washed nectary. The attraction of the sugar evidently then acts by exosmose 

 on the water contained in the tissue of the nectary; and we may well assume 

 with Wilson that even in the normal condition of the nectary, the solution of 

 the sugar already excreted affects the cell-sap of the nectary osmotically, especially 

 when the sap already excreted becomes by evaporation more concentrated than 

 the solution in the tissue of the nectary. The excretion of the nectar in the first 

 instance, however, must depend upon other causes: either, as has been supposed^, 

 the outer wall of the nectar-cells becomes transformed into a soluble product, as 

 in the coUeters of leaf-buds, or, in so far as this is not the case, a pressure similar 

 to the root-pressure forces out the sap. 



' Respecting the mechanics of the secretion of nectar, cf. 'The Cause of the Excretion of Water 

 on the Surface of Nectaries,'' by Dr. W. P. Wilson (Cambr. Mass., U. S. A.). The matter, however, 

 needs further investigation. 



