93 



the plant TDody and will describe them briefly in the following. 



1. The duct tyloses are best known:- They are the ones 

 which fill the lumina of the ducts and tracheids and are pro- 

 duced by hypertrophy, of the living parenchjTna cells lying in 

 the wood. 



The knovdedge of duct tyloses dates back to 

 Malpighi, who foujid "oval and translucent little 

 sacs" enclosed in the ducts of Quercus^l The un- 

 named author in the Botanische Zeitung« investi- 

 gated their anatomy carefully. In his statements 

 the development of tylose,^ from parenchyma cells is 

 excellently described. Bohm® sought to explain the 

 production of the tyloses, first of all, by an ac- 

 eumula^ion of cytoplasm between the lamellae of the 

 duct v/alls , whose innermost layer grows out to form 

 the membrane of the tylose cell. He traced it back 

 later to an excretion of protoplasmic drops and their 

 subsequent hardening. 



The form of the tyloses is determined in the first place 

 by the nature of the thickening of the duct wall. If ring- 

 like thickenings are present the adjacent parenchyma calls 

 may produce a broadly-based outgrowth into the lumen of the 

 duct, (Compare fig, 29). The conditions in the spiral duets 

 are similar, if the single spirals are not too flat, and the 

 thin membrane places are not too narrow, (Compare fig. 30), 

 If the ducts have bordered pits, only very narrow entrances 

 into the lumina of the ducts lie at the disposal of the grow- 

 ing parenchsmia cells. The body of the original cell and the 

 (100) newly produced appendage are then united only by a narrov/ 



isthmus, (Compare fig. 31) . The form of the tyloses depends 

 still further upon vi^hether the parenchyma cells grow out 

 '''into the lumen of the duct, forming only one tylose for each 

 cell (fig. 31) or several at the same time (figs. S9 and 30) 

 whether therefore one or more appendages are produced on one 

 and the same parenchyma cell. Further, the spg,ce available 

 in the interior of the duct is of importance. Usually many 

 tyloses push against one another in the same duct g,nd fill 

 the lumen with a pseudo-parenchymatic tissue, while they are 

 flattened agimnst one another making necessary a polyhedric 

 form, (fig^'31>. If the number of tyloses is small, they fill 

 the lumen of the duct, as round bladders or cylindrical sacs. 

 Complicated forms arise, if the tyloses grow out from one 



1, Anatome Plantarum, 1675-1679, Tab, TI , Fig. 21. 

 Compare the translation by Mobius, Eiassiker d. exakten Wiss- 

 ensch. Herausgeg. v. Ostwald, 1901, Bd. CXX, p. 7, 32, 



2, Unters lib, d, zellenartigen Ausfullungen der Gefas&e, 

 in place msntioned, 1845, Bd, III, p. 2E5. 



3, Ueb, Funktion und Genesis d, Zellen in d. Gefassen 

 des Holzes, Sitzungsber. Akad. Wiss, Wien, 1867, Bd. LV, Abt. 

 II, p. 851. Ueb. d. Funktion d, vegetabil, GefSsse. Bot, Zeitg. 

 5.879, Bd, XXX^fll, p. E89, 



