348 



THE INDIA RUBBER WORLD 



[August i, 1902. 



THE LATEX BEARING DUCTS OF THE RUBBER TREE. 



By Henri Lecomte. 



T'*HE latex of the caoutchouc plants is contained in lactici- 

 ferous channels, whose distribution varies with the na- 

 ture of the plant and perhaps also with its biological 

 conditions. It is evident that an exact knowledge of 

 the distribution of the laiicifers (the latex bearing ducts) is in- 

 dispensable for fixing the regulations of methodical work. Un- 

 fortunately, this study has been neglected, sothat the processes 

 of extracting the latex are altogether empirical. My present 

 intention is not to consider all the cases that may arise, but 

 simply to call attention to certain facts and considerations, 

 which may enlighten experimenters in their researches. 



For example in the Landolphia Heudelotii, which furnishes 

 the larger part of the caoutchouc exported from the Senegal, 

 the Soudan, and Guinea (in west Africa), it is easy to recognize 

 from a cross section of the liatte (climbing plant), that the 

 laticifers are especially distributed in the middle portion of 

 the bark, but are almost altogether lacking in the outer por- 

 tion, as well as in the zone nearest the wood. 



To reach the laticifers, there is therefore need of pene- 

 trating through the bark. The laticifers of the Landolphia 

 Heudelotii are long tubes, ramified and anastomozed, whose 

 diameter varies from 30 to 45 thousandths of a millimeter. 

 These laticifers extend principally along the stem, but, as I 

 have said, they are ramified, and these ramifications take a 

 direction more or less oblique. 



A transverse section a i, of determined length and depth, 

 may, for example, encounter a number of laticifers and pro- 

 duce a proportionate number of orifices from which the latex 

 will flow. A longitudinal incision c d, of the same length and 

 depth, will meet a much smaller number. 



The inspection of the hgure (i) will render further explana- 

 tion superfluous ; but it is not difficult to demonstrate the fact, 

 at least in the case of the Landolphia Heudelotii. It is known 

 — and this is the point of departure 

 of the processes of the extraction 

 of the caoutchouc from dry bark — 

 that the latex coagulates sponta- 

 neously in the laticifers of the bark 

 when it dries, so that each laticifer 

 of dry bark contains a very thin fil- 

 ament of rubber. If a piece of dry 

 bark is broken, and the two frag- 

 ments separated carefully, they are 

 seen to be united by a multitude of 

 rubber filaments, the number being 

 equal to that of the laticifers en- 

 countered by the section (Fig. 2). 



Let this section be made perpen- 

 dicularly to the length of the stem, 

 or parallel to this length : the fila- 

 mets are still found in large num- 

 ber if the section is crosswise, but in 

 small number only if it is longitud- 

 inal. Fig. 3, drawn from nature, 

 exhibits this clearly. A piece of 



• Translated from the Journal d'Aficutturi Tropicale iPaiis, April 30, 1902) 

 for The Inbia Rubber World. The suggestions contained in this article were 

 presented in a popular lecture on " Caoutchouc and the Plants which Furnish It," 

 delivered by this botanist at Paris, on March 4, under the auspices of the French 

 Association for the Advancement of the Sciences. 



Theoretic representation of 

 the arrangement of the lati- 

 cifers. 



a b — Cross section meeting 

 six laticifers. 



c d — Longitudinal section 

 meeting only one laticifer. 



FIG. 2. 



Two pieces of bark broken 

 apart crosswise, but still con- 

 nected by a large number of 

 caoutchouc filaments. 



bark of rectangular form was sepa- 

 rated in two parts by a perpendic- 

 ular section along the length of the 

 stem ; the two portions were still 

 connected with numerous filaments 

 of rubber. If one of these fragments 

 was aftei wards broken in two parts, 

 by a section parallel with the axis 

 of the stem, and the two parts a and 

 b separated, as shown in Fig. 3, they 

 were seen to be connected by a 

 small number only of thin threads 

 of rubber, because such a section 

 meets a much less number of latici- 

 fers than a cross section of the same 

 extent. 



We may, therefore, consider it 

 demonstrated that two equal incis- 

 ions made in the bark will encounter 

 very different numbers of the lati- 

 ciferous ducts, according as the sec- 

 tion is longitudinal (few laticifers), 

 or transverse (many laticifers) ; it is 

 not difficult to conclude that the 

 cross section will cause a much 

 greater quantity of the latex to flow 

 than the longitudinal section. This 

 is very easily shown on living climb- 

 ing plants belonging to the genus 

 Landolphia. 



I have also verified the fact on a 

 young Castilloa elastica, which was 

 placed at my disposal by Messrs. de 

 Vilmorin. Dr. Morris, in his Cantor 

 lectures, published in Iht Journal 0/ 

 the Society of Arts (London), has 

 stated that in the trees of the genus 

 Heiiea, cultivated in the Henarat- 

 goda garden in Ceylon, other things 

 being equal, the oblique incisions 

 (45°) produced about twice as much as the vertical incisions. 



The transverse incisions have another advantage with refer- 

 ence to the gathering of the latex. In consequence of the con- 

 stant growth of the ligneous cylinder surrounded by the bark, 

 the latter, not following this growth, is stretched more and more, 

 like a too narrow garment, around too voluminous a body. It 

 is this tension of the bark which causes the longitudinal cracks, 

 so characteristic, for example, of the surface of the bark of an 

 oak tree. If an annular cross band of bark is removed from 

 the trunk of a tree, and the attempt afterwards made to replace 

 it at the spot from which it was taken, the two extremities will 

 not meet. 



It is precisely this tension which causes the flow of the latex, 

 which the capillarity would keep, in the absence of this inter- 

 vention, in the interior of the laticiferous ducts. In making 

 a cross section, the tension of the tissues above and below this 

 section is not modified. The result is that the latex will flow 

 as freely as possible. A longitudinal section, somewhat ex- 

 tended, would, on the contrary, produce different results, for 



FIG. 3. 



Illustration exhibiting the 

 c.ioutchouc filaments connect- 

 ing two strips of bark. 



Between a and b, the fila- 

 ments proceeding from the 

 transversal inosculations. 



Between a b on one side and 

 c on the other, the filaments 

 correspond to the laticifers 

 encountered bv a cross-section. 



