66 ANATOMY OF THE GYMNOSPERMS 



Pits occur in this position in 71.7 per cent of all the investi- 

 gated species, and their absence in 28.3 per cent points to some 

 special features in development which may be assumed to have 

 a general bearing upon the questions of descent and relationship. 

 In Dammara, as represented by the one species D. australis, such 

 pits are a prominent and characteristic feature, but in the nearly 

 related Araucaria they are remarkable for their uniform absence. 

 In the primitive Gingkoales they are also present, but among the 

 Taxaceae, while generally present, they are occasionally wanting, 

 as in Torreya taxifolia and T. nucifera, or in 66.6 per cent of 

 the investigated species of that genus. Nowhere else among the 

 Coniferales do we find such a feature until we reach the genus 

 Pinus, the second and higher section of which is almost invariably 

 characterized by their absence, thus presenting an exceptional 

 feature to the extent of 68.3 per cent of that genus. That such 

 absence represents a process of obliteration conformable to De 

 Bary's law cannot be doubted, while the sporadic recurrence of 

 this feature in often widely separated genera, or in particular spe- 

 cies of a given genus, must be held to have a more or less direct 

 bearing upon the general course of development. This is empha- 

 sized by the observation that in Larix americana and L. lepto- 

 lepis, as also in Picea bicolor, there is a more or less pronounced 

 tendency to an obliteration which is never fully developed. This 

 is expressed in the somewhat remote position of the pits and 

 their very small size, which renders them obscure and often diffi- 

 cult to discover. In this respect these species represent transi- 

 tional forms. 



As an exceptional feature bordered pits may sometimes be 

 found upon the tangential walls of the spring wood. This is espe- 

 cially noticeable at the ends of tracheicls, and in rare cases it 

 may apply to the entire extent of the wall. The most notable 

 instance of this kind, because practically unique, is to be met 

 with in Sequoia gigantea (figs. 1 2 and 1 3). Those spring tracheids 

 which lie in direct contact with the summer wood of the pre- 

 vious year often exhibit this feature with great prominence, but 

 it may also extend radially through several successive tracheids. 



