>i 



MR. W. CARRUTHERS ON FOSSIL CYCADEAN STEMS 



disarticulated near the item, as in Cycas and Zamia, and have not left any length of per- 

 manent bases of the petioles surrounding the axis like what is seen in Encephalartos and 

 some fossil genera. The scars are not all of the same size. Those on the swollen por- 

 I ns of the Stem arc large and rhomboidal, while on the constrictions they are as broad, 

 but much less deep. The whole surface of the large scar forms the cicatrix from which 

 ( I i ppendage which it bore has been broken off. The scars on the lower half of the con- 

 itrictod portions of the stem are smaller than those on the upper half, being from six to 

 .•i-ht time, as broad as deep; they are slightly imbricated, and the cicatrix is confined 

 to the upper margin. The scars on the upper portion of the constriction are from two 

 to four times as broad as deep, and the cicatrix extends over the whole exposed surface, 

 besides these impressions of the outer surface of the stem, there are found sometimes 

 aclosed in them, but more frequently independent of them, cylindrical columns covered 

 with interrupted longitudinal ridges. These ridges represent the meshes or openings in 

 the woody cylinder through which the vascular bundles passed to the leaves. Such 

 openings are found in all dicotyledons, but are especially obvious in those which have a 

 large medulla associated with a slender wood-cylinder and numerous large leaves, as in 

 Th pa and in the Cycadece. It is only in the Cycadece that such markings are associated 

 with the rhomboidal scars described as characteristic of the outer surface of the stem. So 

 < letly, indeed, do the corresponding parts agree, as far as they can be compared, that 

 there can be no doubt that Bucklaudia was built upon the same plan as Cycas. The 

 best speri $ for comparison is C. circinalis, Linn., not only because it is often met with in 

 cultivation, but chiefly because Miquel has, in an elaborate memoir 1 , investigated the 

 cause* of the swellings and constrictions, and the different forms of scars associated with 

 them on the stem of this species. He shows that they are produced by the peculiar ter- 



minal inflorescence of the plants. The seeds are borne on the margins of altered lea"v 



and the terminal crown of the fruit-bearing leaves is separated from the true leaves by a 

 large number of lanceolate scales arranged in the same series with the leaves. In C. cir- 

 cmalit no scales occur among the true leaves, they are entirely confined to the con- 

 stricted portion of the stem. The differences in the size of the stem are the results, ac- 



ordim? to Miquel, of the different appendages borne upon these different parts. The inter- 

 nodes are not developed in the stem of Cycas, so that when the bud is completely formed 

 the axis does not lengthen. It increases, however, in diameter during its whole life, 

 chiefly by the development of the cortical parenchyma ; and as this is intimately related to 

 th scah- and leaves, the true leaves develope more than the scales or fruit-bearing leaves, 



tnd consequently produce a greater thickness in the portion of the stem immediately 

 mnected with them. 



The remarkable correspondence between the recent and the fossil stems, both belonging, 

 as there can be no doubt, to the same order of plants, may fairly be inferred to have been 

 1-rodue I by the same cause:— that the large scars are the bases of true leaves ; the smaller 

 Mat* immediately succeeding them, as is established by their slight imbrication and the 

 small cicatrix on their upper margin, supported lanceolate scales ; and the somewhat larger- 



Nat. seT ll\l\\ ^l { ' " U) P ' 125 ' PlS ' iV "" Vi " Tranalated b 3" Brongniart, and published in the Ann. des Sc. 



