318 The Philippine Journal of Science 1923 



idioblasts in identification, as their presence and abundance are 

 undoubtedly influenced by various factors, such as soil chemistry 

 and root absorption. 



Mention has already been made of the gross features and 

 distribution of the resin cysts in the dipterocarp group. They 

 arise schizogenously through the fission of parenchyma cells 

 and are borne in series which simulate the resin canals of the 

 conifers. In the majority of the Philippine dipterocarps the 

 series are restricted to a vertical alignment, and the various 

 rows of cysts are arranged in interrupted lines which extend 

 tangentially ; but in certain species the solitary arrangement 

 prevails, either wholly (Vatica) or in part (Dipterocarpus and 

 Anisoptera spp.) . Horizontal resin cysts are very rarely pres- 

 ent, having been observed in but one (Shorea mindanensis) of 

 the twenty-four species examined. 35 They are confined to the 

 wood rays and, as seen in tangential section, appear as small 

 apertures encircled by minute epithelial cells which are in turn 

 bordered by normal ray cells. In contrast to the conifers where 

 normally but one duct is found in a given ray which is thereby 

 altered in contour (fusiform), the rays of Shorea mindanensis 

 sometimes include two series of cysts but the ray remains 

 unchanged in form. The evolutionary significance of the 

 absence of horizontal resin cysts in the Philippine dipterocarps, 

 aside from Shorea mindanensis, remains to be determined. 



As seen transversely, resin cysts vary little in shape and size 

 in the various species and little diagnostic value can be attached 

 to such variation. Isolated cavities are usually rounded, while 

 those of the tangential rows are compressed tangentially. Size 

 manifests itself only in relative conspicuousness and is of little 

 value, owing to the irregular distribution of cysts. Vatica is 

 characterized by small resin cavities, while the other extreme 

 is represented by Dipterocarpus. 



In the following pages I have handled the subject somewhat 

 differently from other investigators in that I have made the 

 keys to lead to well-established commercial groups rather than 

 to natural genera, for the sole reason of making the keys 

 conform with the classification in the trade as well as in the 

 forestry regulations in as much as government charges on such 

 timbers are based on these groups. 



"Pfeiffer (footnote 25) reports horizontal resi 

 nese dipterocarps. I have also observed them 

 and Federated Malay States. 



