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pies about four fifths, the other the remainder ; if these tissues of un- 

 equal density occupied an equal share of the organ, a strong curve 

 would be the result ; but as the Er odium has no aperture to eject the 

 seed if there were a sudden jerk attending its separation, that act is 

 not required, consequently the apparatus for disengagement is some- 

 what modified. 



It appears from observations that besides this arrangement for pro- 

 ducing an alteration of form, that there exist some peculiar hygro- 

 metric properties ; for when longitudinal sections of this portion are 

 placed under the microscopic and water is added, they do not appear 

 to expand equably, one side expanding before the other, and appear- 

 ing to slide in advance of it. If this be the case in the entire organ, 

 it is readily seen that it is obliged to accommodate itself to the spiral 

 form by losing the moisture from its tissue. 



By far the most curious set of hygroscopic actions are manifested 

 in the expansion of the pappus or seed-down of some plants belong- 

 ing to the order Composites. The calyx of the florets of these plants 

 does not put on the leafy character common to most flowers, but is 

 composed of many curiously constructed feathery hairs, which appear 

 to be the representatives of that organ in a very rudimentary condi- 

 tion ; and by the design of Nature is destined to serve a most curious 

 part in the dissemination of these plants. When the seed-down of 

 Cnicus eriophorus is examined in its natural situation, it is found to 

 be arranged on the apex of the fruit, like the hairs in a pencil brush, 

 crowded amongst hundreds belonging to other florets, and so com- 

 pressed by those by which it is surrounded, as to be unable to expand 

 the numerous parts of which it is composed ; but by the continued 

 drying of the tissues the whole mass of seed-downs partakes of the 

 same struggle to expand their rays, and coupled with the contraction 

 of the receptacle on which they are situated, the numerous mass be- 

 comes at length detached. When freed from the pressure of each 

 other, the heat of an autumn day causes the expansion of the several 

 filaments, which, radiating from the same centre, soon arrange them- 

 selves into a globular figure, the seed being attached to the centre. 

 In this state each becomes the sport of the wind ; the passing current 

 wafting it from its place of birth, bears it away, and it obeys the dic- 

 tates of the element till the breeze slackens, when it descends slowly 

 to the earth, and if the place of its descent be charged with moisture, 

 then its career is stopped, that becoming either the place of its growth 

 or of its destruction. 



Such is the nature of the office of this seed-down, but the most in- 



