CAPILLARITY AND ROOT-PRESSURE. 271 



contents for the fluids in the nutritive earth, the more abundantly and energetically 

 will this be carried on. The phenomenon can be well seen in some moulds, 

 especially Mucor Mucedo, which makes its appearance in such quantity on 

 succulent fruits; and in the mycelium of the so-called Dry-rot, Merulius lacry- 

 mans. Fluids are sucked up by the lower portions of the tubular cells which cover 

 the nutritive substratum, and expelled again through the walls of upper parts 

 of the same cells, which project freely into the air. These upper portions of the 

 mycelium cells appear as though ornamented with tiny dewdrops, which in the 

 case of the Dry-rot coalesce and attain to a considerable size. Damp woodwork in 

 cellars, where this fungus has established itself, is often thickly besprinkled with 

 the drops which have been excreted on the surface, and if a lamp is brought into 

 the darkness, and the infected places illuminated, hundreds of these tiny drops 

 sparkle and glitter like the "jewels" in a cave of stalactites. Suppose then that 

 such a cell, one wall of which allows fluid to enter, is attached by the wall opposite 

 to that through which the fluid enters, to another cell; then this second cell will 

 absorb the liquid, and, if tubular, the sap may rise higher and higher in it, and by 

 the pressure of the liquid continually arising from below, even be forced through 

 other higher cells which are capable of filtration. Naturally the rising current of 

 sap thus generated follows the line of the least resistance; if then the cell-tissue 

 where this action terminates is perforated by canals ending in pores on the surface, 

 the fluid will emerge from these pores in the form of drops. This actually happens 

 not only in many large-leaved Aroids, but also in plants growing in the open 

 country if the air which passes over the leafy parts above the ground be very 

 humid, and the soil in which the roots are buried proportionately warm. In many 

 plants with succulent foliage, drops of water may be seen issuing from the thin- 

 walled cells and pores of the leaves when the almost saturated air becomes cooled 

 after sunset, while the soil, round about the absorbent roots, having been exposed 

 all the day to the sun's rays, retains its higher temperature. Young blades of 

 corn have rows of such drops, which look exactly like dewdrops, and have often 

 been mistaken for them. This extrusion of water from the leaves can easily be 

 produced artificially by placing the plants in a saturated atmosphere, and at the 

 same time slightly warming the earth round the roots. There is no doubt that 

 the sap which exudes from the leaf -pores originates in the nutritive soil, and is 

 taken up by the absorbent cells of the root; from these the vessels and cells of 

 the main root and stem, through which the sap can filter, carry it up to the leaves. 

 If, therefore, we cut across a stem a little distance above the ground, we shall see 

 the sap, which has already accomplished half its journey, welling up as drops on 

 the cut surface; i.e. we shall see the remarkable phenomenon called "weeping", 

 of which mention has already been made. The quantity of sap which flows 

 from such a cut surface is in many cases astoundingly great. In Java certain 

 Cissus plants, belonging to the family of lianes and living in damp woods, are 

 actually made use of as vegetable springs. The watery sap flows so abundantly 

 from a cut branch that in a very short time it will fill a glass, and forms a cool and 



