H. von Mohl on the Formation of Gum-Tragacanth. 163 



sion, that the tragacanth-shrubs, exposed to the glowing heat 

 of the sun by day, rapidly absorbed the moisture of the clouds 

 and fogs, and that the tragacanth, greatly swollen by the moist- 

 ure of the fogs and dew, broke out through the pores of the 

 bark, and exuded in the form of curled worms. 



Labillardiere^s observation furnished DeCandolle* with an 

 opportunity of explaining in a somewhat different manner the 

 way in which tragacanth is squeezed out. He compared this 

 exudation of tragacanth with that of Nemaspora crocea (which 

 he at that time regarded as a gum, and not as a fungus) from 

 the bark of the beech-tree, when kept in a damp place. He re- 

 tained this view in his ^Physiologic' (i. p. 175), after he had 

 recognized that Nemaspora was an independent plant, having 

 convinced himself that the eruption of Nemaspora on dead 

 trees was connected with the moisture of the atmosphere, and 

 concluding from this that the action of moisture caused the wood 

 to expand more than the bark ; the wood being thus as it were 

 compressed in a sheath, squeezed out upon the surface any slimy 

 substance lying in the inner part of the bark. This explanation 

 did not meet with any favour from Treviranusf, who assumed 

 that the exudation of the gum depended upon increased secretion. 



The botanists above mentioned, as also the most recent phar- 

 macologists (for instance, Pereira) had not the slightest doubt 

 that tragacanth was a mucilaginous juice secreted by the plant. 

 KiitzingJ, from the microscopic examination of exuded gum, 

 set up the view that it was an independent organism, a fungus, 

 composed of starch-bearing cells, among which lay the fibres of 

 the parent-plant. The walls of these cells were described as 

 consisting of many thick layers, composed of bassorin, and 

 lined by a delicate membrane composed of cellulose. We look 

 in vain for any proof that these cells are of Fungal nature; 

 although such would be anything but superfluous, for Fungi 

 with cellulose membranes and starch-granules would be not a 

 little remarkable. 



linger § ascribes a totally different origin to gum-tragacanth, 

 stating that it is formed of the secondary layers of the medullary 

 rays in several species of Astragalus. 



I know of no other microscopic investigations of tragacanth 

 which teach anything ; those of Guibourt [| are devoid of interest. 



Seeking for an explanation of the nature of gum-tragacanth, 

 I regarded it as of primary necessity to examine, not the gum 

 occurring in commerce, but the stems of a large number of spe- 

 cies of Astragalus of the section Tragacantha. Unfortunately 



* Astragalogia, 1802, p. 12. t Physiologic, ii. p. 21. 



X Philos. Botanik, i. 203. § Anat. u. Physiol, d. Pflanzen, 119. 



II Hist, natmelle des Drogues simples, 4 edit. iii. p. 420. 



11* 



