450 



Journal of Agricultural Research 



Vol. I, No. 6 



branches, twigs, roots, leaves, vines, herbaceous plants like the squash, 

 or on such of the lower forms as ferns, 1 and did not cover to any extent 

 the American species. 



The method of examining the wood was as follows: The ends of the 

 logs which form the collection of commercial American woods (PI. LIX, 

 fig. i) of the Forest-Products Laboratory were examined with a hand 

 lens. Blocks cut from these were also studied microscopically. Small 

 strips extending from the bark through the trees to the pith, including 

 the sapwood, the so-called transition region, and the heartwood, 2 were 

 cut from the logs. Microtome sections about i inch by one-half inch 

 in area and 5 to 20 micromillimeters in thickness were cut from the three 

 planes, transverse, radial, and tangential, taken from each of these dif- 

 ferent regions and were studied under the compound microscope. The 

 observations for hardwoods are given in Table II. Stains were often 

 employed to differentiate the tissues, and macerations were made with 

 potassium hydroxide or chromic acid for special studies of the relations 

 between the tylose and the parenchyma cell producing it. Fresh mate- 

 rial from seedlings and branches was also examined, in order to deter- 

 mine whether the sapwood tyloses were of normal or abnormal origin. 



The Forest-Products Laboratory collection of woods begun in 1910 is 

 not yet complete, and in many cases only one log of a species was available 

 for study. Nevertheless, the majority of the commercially important 

 species are included in the laboratory collection, and in addition to the 

 study of these it was possible to make further observations on authentic 

 material of a number of other important species. Moreover, whenever 

 two or more specimens of the same species were examined, results were 



1 This list of the plant genera where tyloses have been found in wood, roots, leaves, or other portions is 

 given by Kiister. It includes Molisch's observations on the Vienna wood collection and other material 

 as well as those of other authors, whose names are given in parentheses after the genera they investigated. 



Portulacca. 



Prunus (Wieler). 



Pterocarya. 



Quercus. 



Rhus. 



Ricinus. 



Robinia. 



Rosa (Maiile). 



Rubia. 



Rumex (Dutailly). 



Salix. 



Sambucus. 



Santalum. 



Schinus. 



Sideroxylum. 



Solanum. 



Sparmannia. 



Strelitzia. 



Styinatophyllum. 



Taraxacum. 



Thunbergia. 



Ulmus. 



Urtica. 



Vitis. 



Xanthoxylon (Tison). 



2 The cross section of a mature tree may be divided into at least two regions: The outer or last-formed 

 rings, variable in number, which are termed the "sapwood" or "alburnum," and the inner rings around 

 the pith or center of the tree, which in dry material are sometimes indistinguishable in appearance from 

 sapwood, but which are more often definitely marked by a difference in color and are then termed the 

 "heartwood" or "duramen." (PI. LIX, fig. i.) 



