June, 1915.] ^ Ray Pits of Conifers. 545 



its physiological functions, and are so disposed that, so far as it 

 has been possible to observe, they come in contact with each individual 

 tracheid of the wood. It is not uncommon to find tracheids which 

 show four or five points of contact with the ray system. The 

 ray system, is, in turn, through the direct contact of each of its 

 component rays with the cambium and the phloem, in communi- 

 cation with the leaves and all other living structures throughout 

 the tree. 



The ray pits formed at the point of contact of the storage cells 

 with the wood tracheids exhibit a number of variations which 

 seem to be related to the life conditions of the species. Unlike 

 the tracheid pits, they differ widely in shape, size, and number 

 for the different genera and species of conifers, affording both 

 generic and specific points of distinction of high taxonomic value. 

 In Larix and Picea, however, these constant characters are similar, 

 especially in P. sitchensis and L. occidentalis, where the ray char- 

 acters are insufficient to separate the two genera. For this 

 reason, together with the fact that the two genera have widely 

 different habits of nutrition, the two genera have been selected 

 for comparison, since a more direct comparison of the variable 

 characters is possible with woods similar in structure than where 

 the problem would be complicated by structural differences. 



In leaf habit, differences are at once apparent that are asso- 

 ciated with differences in the storage of reserve and in other 

 processes of nutrition of a fundamental character. The leaves 

 of Larix remain through but one season; being a deciduous conifer, 

 the entire foliage must be regenerated each year. In Picea, 

 the leaves remain for 4-7 years, or the spruce is only ){ to K 

 deciduous, and needs to regenerate ){ or less of its foliage each 

 year. Larix, as with other deciduous trees,* is totally dependent 

 upon reserve food for the regeneration of its leaves. Such re- 

 serve is stored in the ray system and a heavy demand will there- 

 fore be made upon the rays early in the season. Picea, on the 

 other hand, could probably meet this need partly, if not wholly, 

 by the newly formed products of assimilation, since it has been 

 found that first, second, and third year leaves of conifers begin 

 to fonn starch by the middle of March, even when the temperature 

 often falls below 0° C.^ Picea, then, should make a relatively 

 slight demand, early in the season, upon the stored reserve. 



To determine the relative difference in the amount of starch 

 stored by Larix and Picea, trees of Larix decidua and Picea excelsa 

 ten inches in diameter and growing on the Ohio State University 

 Campus, were felled during winter and the volume of starch 



4. Lutz. 1897. Biisgen's Bau und Lebenunserer Waldbaumc, p. 196. 



5. Mer. 1885. Ueber eine Methode zur Beobachtung der Assimila- 

 tion. Landwirtschaftl. Jahrb. 



