STRUCTURE.] BULBS OF MARCHANTIA. 257 



hairs,, nor elevated veins, acquires all those characters in 

 consequence of its inversion. * 



A very curious observation , in connection with this subject, 

 has been made by Mirbel, in his memoir upon the structure 

 of Marchantia polymorpha. The young bulbs by which this 

 plant is multiplied are originally so homogeneous in structure, 

 that there is no apparent character in their organisation to 

 show which of their faces is destined to become the upper 

 surface, and which the under. For the purpose of ascer- 

 taining whether there existed any natural but invisible pre- 

 disposition in the two faces to undergo the changes which 

 subsequently become so apparent, and by means of which 

 their respective functions are performed, or whether the 

 tendency is given by some cause posterior to their first crea- 

 tion, the following experiments were instituted : Five bulbs 

 were sown upon powdered sandstone, and it was found that 

 the face which touched the sandstone produced roots, and the 

 opposite face formed stomates. It was, however, possible that 

 the five bulbs might have all accidentally fallen upon the 

 face which was predisposed to emit roots ; other experiments 

 of the same kind were therefore tried, first with eighty, and 

 afterwards with hundreds of little bulbs, and the result was 

 the same as with the five. This proved that either face was 

 originally adapted for producing either roots or stomates, and 

 that the tendency was determined merely by the position in 

 which the surfaces were placed. The next point to ascertain 

 was, whether the tendency once given could be afterwards 

 altered. Some little bulbs, that had been growing for twenty- 

 four hours only, had emitted roots ; they were turned, so that 

 the upper surface touched the soil, and the under was exposed 

 to light. In twenty-four hours more the two faces had both 

 produced roots : that which had originally been the under 

 surface went on pushing out new roots ; that which had origi- 

 nally been the upper surface had also produced roots : but in 

 a few days the sides of the young plants began to rise from 

 the soil, became erect, turned over, and finally recovered in 

 this way their original position, and the face which had origi- 

 nally been the uppermost immediately became covered with 

 stomates. It, therefore, appears that, the impulse once given, 

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