266 THE AMERICAN NATURALIST. [Vol. XXXVIU. 



such cases becomes most pronounced. Instances such as 

 those afforded by Piniis ^trobus and P. 

 itisignis may, according to this interpreta- 

 tion, be held to represent the final phases 

 in the obliteration of the original spirals, 

 and they therefore constitute characters 

 indicative of the highest type of develop- 

 ment. In a few cases the structure of the 

 bordered pit presents exceptional forms. 

 In CupressiLS nootkatensis the pit orifice 

 shows either unusual want of regularity 

 in outline and marked eccentricity of posi- 

 tion, or it is so enlarged as to leave only a 

 narrow border to the round or oval pit 

 (Fig. 14). Similar features occur occasion- 

 Fi<;. l^,.-c^^pressus nootkaten- ally in Other gcucra, aud they are generally 

 deforme^bideSpitfris? ^onspicuous in Puuis tcsda. De Bary (9, 

 p. 159) has directed attention to the same 

 feature in Ephedra and Piuus sylvestris, and he 

 correctly interprets it as a form of arrested devel- (T) 

 opment. Alterations also arise as a feature of ((\ 

 secondary growth in those cases in which the wall A ^ 

 acquires unusual thickness. This is typically the © ^ 

 r cubensis where in plan (Fig. 15), the 

 orifice is extended vertically to a 

 length often twice the diameter of fig. 15.-/V- «^'^^«- 

 the original pit. In tangential sec- shoSig 

 tion, according to the particular deformed bor- 

 direction of the plane of section 

 (Fig. 16), the orifice is either of 

 uniform width, or it enlarges constantly through 

 the entire thickness of the later growth, from 

 ^ within outwards. That such unusual forms are 

 sis. Tangential sec- featurcs of extreme, secondary growth of the 

 asTn Fig.°V^'*x ^^^^^^ ^^id that they may be anticipated in all 

 cases where such modifications of the walls 

 occur, is a reasonable deduction from the observed facts. 



