<5o 



Dr. W. C. Williamson on 



Large Cortical Trache^eal Bundles. 

 Varied conditions.* 



Transverse* 



Double type, without secondary xylem. 

 D.-p. 383, Fig. 17Z, C.N. 1 187. 



Single type, without secondary xylem. 

 C.N. mi. 



Double type, with secondary xylem. 



One with and one without secondary xylem. 

 C.N. 1114. 



Both Bundles, with secondary xylem. 

 D.— p. 387, Figs. 19, 20, C.N, 1 134. 



Single type, with secondary xylem. 

 See C.N. 11 13. 



FERN PETIOLES, PRIMARIL YRA CHIOPTERIS ASPERA. WILL. 



Of these I have sections from the broad bases, and 

 from the ultimate twigs bearing the leaflets. 



Base of Petiole. 

 Transverse. 



F.— p. 679, Fig. 1, C.N. 117. A p. 682, Fig. 6, C.N. 118. 



Smaller Branches. 



R.— p. 90, Fig 2, C N. 1854. 



Transverse. 



R.— p. 90, Fig. 1, C.N. 117. p. 91, Fig. 7, C.N. 1191. 

 F.— p. 682, Fig. 7. See C.N. 119*, p. 682, Figs. 8 and 9, See C.N. 

 135, 1191 .p 



Longitudinal. 



F.— p. 680, Fig. 2. See C.N. 124, 125, 127'. R.— p. 91, Fig. 8, C.N. 

 1856. See also 1855. 



* The number, arrangements, and forms of these are most easily studied in fairly perfect 

 transverse sections of the stems, in which we find seven modifications. I have noted their 

 characteristic features in seventeen such sections. They are most commonly grouped in 

 pairs, located in the innermost cortical zone, each pair being in more or less close contact. 

 The above seventeen sections have furnished twenty eight examples in this condition. Some- 

 times we find solitary bundles, but such are otherwise undistinguishable from the twin ones. 

 Of these I have recorded nine in the seventeen sections. We occasionally find a pair, one 

 of which is in its normal condition, but where the peripheral surface of the second one is 

 furnished with a variable number of secondary tracheaeal laminae arranged in a fan-shaped 

 manner. In three instances I have found both the bundles so furnished, and in three 

 examples I have seen the solitary bundles similarly supplied on their external borders. In 

 nearly all the cases where the bundle of primary tracheae has a zone of secondary xylem on 

 its peripheral side I have found a zone of cambium investing its outer surface. In one instance 

 the bundle must have been imbedded in the cambium, because the secondary laminae radiate 

 equally in a star-like manner from the entire periphery of the primary bundle. We occasion- 

 ally find the pair being pushed outwards through the outer cortex of the stem or branch. In 

 such instances the two bundles are always imbedded in a considerable development of cortical 

 parenchyma, which is obviously about to escape as a branch from the periphery of the parent 

 stem. But this is a point that will require a more detailed examination later on — a point that 

 involves the entire question of the position of the Filicinae during the Carboniferous age. 



