416 M. von Martius on the Growth of the Stem of Palms. 



5. The lower extremity is obliquely prolonged below, and termi- 

 nates, in the form of an extremely slender and exclusively paren- 

 chymatous filament, on a peripherical layer. This layer is wholly 

 different from the liber of the Dicotyledons with relation to the 

 history of its development ; it may however be compared to that 

 organic system as regards its constituent elements. 



6. The spot where the upper extremity of the filament enters 

 into the leaf, is either on the same side of the stem by which it 

 makes its decuiTcnce, or on the side diametrically opposite. In 

 this second case the fibre passes throughout the stem. 



7. There are necessarily decussations for each filament. Some 

 decussate the others in the central part of the stem ; others by 

 bending suddenly to enter a leaf on the side of their origin. 



8. The growth is effected in an organic solidarity between the 

 formation of the elementary organs and the laws of the position 

 of the leaves. It is especially this position and the succession of 

 the systems of phyllotaxis (which generally increase by specific 

 complications in each species of palm), that we must regard as 

 the conditions of the modifications in the decurrence of the fibres 

 and the formation of the wood*. 



9. The oldest part of the filaments is not found at either their 

 upper or lower extremity ; they have their most complete deve- 

 lopment in the middle part of their decurrence. Below they con- 

 sist only of parenchymatous cells ; at their upper extremity they 

 are divided into several finer vessels which enter the leaves. 



10. The lower extremity does not extend to the roots ; it does 

 not go beyond the collum, where is the organic separation of the 

 descensus and the ascensus. 



11. The stem becomes more ligneous and harder by the growth 

 of the fibres which ascend and which make their decussations, 

 and likewise the parenchyma between the fibres becomes thicker 

 and harder. The hardening is effected in a direct ratio to the 

 age of the tree ; and as the organic elements first formed and 

 homologous are grouped at the periphery, the stem is harder in 

 its circumference. 



You see that these results are not in contradiction with the 

 ideas propounded by MM. de Mirbel and Mohl ; they however 

 differ in some less essential points. M. Mohl does not mention 

 in his memoir (De Structura Palmarum in Mart. Palm. Brasil.) 

 the passage of the filaments from one side of the stem to the 

 other ; nor has he explicitly declared that they grow in two di- 

 rections, sursum and deor^sum. With respect to the ideas of your 

 illustrious academician, M. de Mirbel, I quite agree with all that 



* I have demonstrated in what manner the four forms of the stem of the 

 Palms, defined by M. Mohl, owe their different organization to the condi- 

 tion of the phyllotaxis, to the number and length of the internodes, &c. 



