THE DISPERSION OF SEEDS AND SPORES. 57 



up, tearing the seed away from the branch. By 

 curving over in another direction the radicle now 

 transfers the seed to a different spot. When the seed 

 has once more been securely fastened, the radicle lets 

 go its hold, curves over again, and applies its 

 adhesive disk to a fresh spot. Should this prove 

 favourable, germination proceeds, and the plant 

 becomes finally fixed ; but if the place be not suit- 

 able, the somersault may be repeated several times 

 over. Seeds of this description, which had fallen on 

 the leaves of a tree, have been observed to remove 

 to a branch in the manner described. The radicle 

 of mistletoe, to which Myzodendron is allied, also 

 develops in an excei)tional manner, and differs from 

 most ordinary roots in not being geotropic. Young 

 roots, as a rule, direct their points towards the 

 centre of the earth ; but the radicle of Viscum is 

 not affected by gravity, for if its seed be fastened 

 to the under side of a branch, the young root, 

 instead of pointing earthwards, directs itself towards 

 the centre of the branch. 



3. Hygroscopic Action and Turgescence. — 

 Hygroscopic movements are brought about by the 

 contraction of tissues in the course of drying. We 

 have an example of this in the warping of unseasoned 

 timber, where the bending is caused by the younger 

 sap-wood on the one side contracting at a different 

 rate from the older heart- wood on the other. Fibres 

 especially are prone to bend and twist as they dry. 

 Every angler knows how cat-gut unbends and 

 straightens when put into water. Advantage is 

 taken of this property in the simple old-fashioned 

 weather-glass, still sometimes to be seen, consisting 

 of a model house having two doors. Good weather is 

 indicated by the appearance of a small female figure 

 at one door, rain by the figure of a man coming out 

 at the other. The figures are attached to a support 

 suspended by a fibre of cat-gut, which twists or 

 untwists according to the state of the atmosphere. 

 The instrument is really a hygroscope or hygrometer. 



