34 HUTCHINSON'S POPULAR BOTANY 



be seen to break through the membranous cell-wall a proof of their 

 remarkable elasticity. In most spiral cells that have been examined the 

 fibres wind from left to right; and it has been suggested with some show of 

 reason that the direction of the twining stems of plants may have definite 

 relation to the direction of the spirals. This would certainly appear to be 

 the case in the Hop (Humulus lupulus}, which is a right-handed climber and 

 alwavs has right-handed spirals. SaccolcMum guttatum, an East Indian 

 species of epiphytal Orchid, has fibres which wind in opposite directions, but 

 this is not a twining plant, 



A fair idea of a spiral cell may be obtained by placing a coil ot fane wire 

 in a tightly enclosing glass tube of the same length as the coil, and covering 

 up the ends with glass discs. In Nature the fibres are extremely delicate, 

 their diameters being in some cases less than yo^th of an inch : and as a rule 



FIG. 57. CELLS FROM THE MISTLETOE (Viscum album). 

 1. Spiral cells. 2. Annular cells. 3. Reticulate cells. 



they are quite transparent and colourless. Nevertheless, they may and do- 

 vary considerably in thickness : and in most plants of the Lily order, and 

 also in the Elder (Sambucus), the coiled-up threads may be seen with the- 

 naked eye. If the stem of a Lily be partly cut across and then gently 

 broken, the chances are that the broken pieces will be held together by some 

 of these delicate threads; and they will probably be found to be strong 

 enough to support the weight of one of the fractured pieces, if the piece in 

 question be not too large. It is wonderful to think that though some of the- 

 cells which contain them measure only ^oV^t-h of an inch in diameter, the tiny 

 spirals may consist of several distinct threads ; indeed, the contiguous coils- 

 in some cases have been found to number more than twenty ! How carefully 

 Nature prepares her work even when the objects of her skill are invisible to 

 the unaided human eye ! 



