548 The Ohio Naturalist. [Vol. XV, No. 8, 



It has been shown that the reserves stored in the rays are 

 forced into the tracheids and are conveyed to the developing new 

 shoots at the beginning of the growing season.® The yearly oc- 

 currence of this temporary current woiild be likely to influence 

 the development of the semi-bordered pits through which it passes, 

 providing such pits had not fully completed their development. 

 Since a period of about 90 days is consumed in the development 

 of an annual ring in Picea and Larix/ the ray pits of any given 

 ring will be of successively greater age with the youngest at the 

 commencement of the ring, in the earliest spring wood, and differ- 

 ing in age at the extremes by 90 days; hence certain of them, it 

 may be assumed, would still be plastic when this current is formed. 

 By way of confirmation, twigs of L. decidua were sectioned May 

 20, when leaves had apparently attained their full size. It was 

 found that the sixth tracheid was then being formed, which would 

 bear out the predicted sequence of the maturity of the ray pits, 

 and be in proper position with respect to the greatly diminished 

 current indicated by the fall of the curve. (Figs. 3 and 4). 



The curves referred to were obtained from measurements 

 taken of the diameter of the ray pits, commencing with the first 

 spring tracheid and ending with the last summer wood tracheid. 

 Such pits will, then, be arranged in series according to age. For 

 sake of coinparison, these measurements are squared, since the 

 efficiency of circular osmotic membranes, other things being con- 

 stant, should be proportional to such values. The accompanying 

 curves plotted from the results so obtained, show graphically the 

 existence of exactly such a variation in size as would be expected 

 had the above outlined modifying influence of the assimilation 

 current been manifest. As anticipated, both species of Larix 

 show an early and strongly pronounced increase in the size of 

 their ray pits corresponding to the probable time, intensity, and 

 duration of the demand made upon the stored reserve, for the re- 

 generation of leaves. Also, the curves of Picea show the expected 

 absence of the early high point. The problem is here complicated 

 by the presence of currents of newly formed assimilation products 

 commencing in March and increasing with the advance of the 

 season; but, in a general way, the shape of the curve is in accord 

 with the probable influence exerted by the later leaf habit of the 

 genus and the absence of growth conditions that would make the 

 early and brief demand upon the stored reserve noted in Larix. 

 The data thus collected has also demonstrated the intimate con- 

 nection of the ray with the vital processes of growth and nutrition 

 and the reaction of such processes upon the structure of the ray. 



6. Fi.scher, Alfred. 1890.^ Pringsheim's Jahrbvichcr, XXII, p. 73. 

 Strasburger. 1891. Uber den Bau und die Verrichtung der Leit- 



ungsbahnen in den Pflanzen, pp. 98, 297. 



7. Hartig, Robert. 1885. Hols der deutschen Nadelwaldbaume. 



