Prof. C. Morren on the discoid Piths of Plants. 75 



the pith was said to be an organ which nourished the stem in 

 its youth in order to aerate it subsequently (Hales) ; or it was 

 that which formed the pistil, the supposed centre of the 

 flower (Linnaeus). Now it is taken for an apparatus which 

 nourishes the fruit, as milk nourishes the young animal, 

 the fruit of the mother (Magnol) ; — now the pith becomes 

 an attracting pump, which draws water from the soil by the 

 vacuum it causes in the branch (Borelli). With one (Mai- 

 pighi) it is a conductor of the sap ; with another (Plenck) it 

 is a reservoir for the moisture which the young branch makes 

 use of in dry weather. A celebrated physiologist (DeCandolle) 

 sees in it a cotyledon of the bud, that is to say an organ which 

 nourishes the bud, as the cotyledon nourishes the plumula 

 which germinates. - Another philosopher, whose views we 

 must confess are very ingenious (Du Petit Thouars), supposes 

 it to be the substitute for the cotyledons ; for where these do 

 not exist (Lecythis) the pith is in excess. 



Now in the midst of these differences of opinion one fact 

 remains certain, which is that the bud has need of pith to be 

 developed, it is its necessary sustentaculum. Raspail knew 

 very well that the evolution of the bud is in reality a germina- 

 tion under other forms. But, if this is become a settled truth, 

 it must be acknowledged that a number of circumstances have 

 remained unknown, and it is precisely the study of discoid 

 piths which will reveal to us some of the most curious. This 

 has induced me to publish at present the results of my ob- 

 servations on these piths, the more so as these remarks have 

 convinced me that if the explanation given by M. DeCandolle 

 of their formation is correct, it must be understood in a cer- 

 tain manner, and a restricted sense must be given to the word 

 rupture; for were we to suppose that a rupture was a rent, a dis- 

 solution of continuity effected with violence and with laceration 

 of cells or of vessels, we should be quite wrong. In the same 

 manner that a fruit opens by a predisposition of the tissues 

 destined to break, that is to say to divide, so a pith perforated 

 with transversal cavities is also thus pierced by & predisposition 

 in the organic elements which lose their continuity by means 

 of a structure appropriated to this purpose. If the text of 

 adopted physiologies were taken literally, we should say that 



g2 



