99 



pension of the negative air pressure in the dticts 

 were the only cause of tyiose formation, then, con- 

 sidering the well-knovm fact that the ducts usually 

 stand in open continuity for far longer stretches.^ 

 often several meters long,- this would have to hold 

 good for much deeper distances," 



She question as to the function of the tyloses in the 

 ducts causes great difficulty. Ihc nature of the tyloses 

 descrihed above make it certain that they influence the fun«* 

 ctionin^ capacity of the ducts of which they have possession. 

 Tyloses v/ill stop up the water conduits by the close filling 

 which they produce in the ducts ' r.nd m.-ike then incapable of 

 "SS^'i^^^^^** ^"^ Seems doubtful, how^evBjB, whether in this 

 effect of tyloses, we may look for their significance from 

 the view of physiological anatomy:- for some oases indeed it " 

 seems improbable. iDhat tyloses are beneficial on the surface 

 of_=?;ounds as obstructive precautions, may indeed be obvious, 

 buu It is inconcievable why an obstruction ox the conduits 

 should also be advantageous; at times in uninjured p&rts;- 

 even in very young sections of shoots. Besides this, cases 

 are not lacking in r/hieh tyloses remain nucsh too small ±o 

 Bake a perfect stoppage, for these reasons, Haberlandt"'" as- 

 sumes that "the tyloses in some way interfere tTith the pro- 

 cess of transporting materials, since they enlarge the contact 

 surface of the parenchj^ma cells and ducts, thus, for example, 

 they could accelerate the compression of hemorrhage in the 

 ducts-, could force jfeugar into these ducts, or conversely like 

 haustoria, which they resemble, could draw out from the trans- 

 piratory current certain substances dissolved in it, Ihe cijv 

 cumstajoces that, according to Heess, the farmation of tyloses 

 often continues a long time in ducts several years old, seems 

 to favor a function of this kind, it appears a6 if the old 

 tyloses., having grown incapable of functioning, are replaced 

 by new ones," Of course, for the present, this is all sup- 

 positio-ji, 



ThuS:, the search for a physiological significance of 

 the tyloses has not yet led to any satisfactory results. Per- 

 haps the assumption brings us nearest to the truth, v;hich 

 suggests that many of these, like the hypertrophies already 

 described, do nothing for the v^ell-being of the whole organism 

 but are to be considered as pathological formations in the 

 sense discussed at the beginning of this book. 



£• The secretion glands and the rosin ganals, like the lu- 

 mina of the ducts and tracheids may be filled up by tyloses 

 through the outgrowth of adjacent living parenchyma cells » 

 imong"the cryptogams (lycopodium) , gymnosperms {ZamX$., Pinus, 

 IiariK, etc.) , and various kinds of angiosperms (Rhus, Hyper- 



1. Physiol, Pflanzenatomie, E. Aufl., 1896, p. 285. 



