758 



SCIENCE. 



[N. S. Vol. III. No. 73. 



The examination of numerous sections, 

 including one only, 1 mm. in cortical diam- 

 eter, of L. nmndum, a low species, shows 

 the same habit of development, and, in 

 the descending from the smallest twigs 

 to larger and lower branches, the same 

 enlargement of the primary stele as a 

 whole and of the number of its com- 

 ponent tracheids as in the other arbore- 

 scent forms. 



The painstaking and exhaustive study of 

 his remarkable series of sections led Prof. 

 Williamson to abandon his earlier views, 

 while approaching in the main to those set 

 forth by Solms-Laubach in his Fossil 

 Botany. The impossibility of intercala- 

 ting leaves and leaf traces among the pre- 

 arranged geometrically disposed spirals and 

 the observed numerical progression of the 

 volume of tracheids in passing downward 

 lead to the inevitable conclusion that, un- 

 like any living type of growth, these enor- 

 moias developments of primary tissue origi- 

 nate at the base of the primary stem close 

 to a growing point. 



Here the chain of corroborative observa- 

 tion ends and the difficulties and further 

 unsettled problems begin. Prof. William- 

 son adds: "As to the magnitude of the 

 primary xylem strand and the enormous 

 number of tracheids which compose it, 

 these equally reached their largest propor- 

 tion at the base of each solitary aerial stem. 

 How such numbers of tracheids, varying in 

 the tjrpe of L. Wunschianum from 4,000 to 

 15,000, could be produced in that position 

 is difficult to understand. The young sporo- 

 phyte could not possibly have contained 

 them; hence some process of growth, of the 

 nature of which we have as yet no knowl- 

 edge, but which was capable of producing 

 these marvelous results, must have suc- 

 ceeded, if not been developed out of the 

 sporophyte." 



The second paper, entitled Sur V utilite de 

 I'Hude des plantes fossiles au point de vue de 



revolution des organes, is by M. B. Renault,* 

 the leader of the French paleobotanical 

 histologists. 



M. Renault draws a very suggestive 

 contrast between the present general group- 

 ing of living plants and what would be ex- 

 pected if the manifest relations of the fossil 

 species were taken into consideration ; for 

 vegetable paleontology shows the existence 

 of vast numbers of individuals presenting 

 in different degrees characters intermediate 

 to those which obtain among the living 

 plants. If the fossils are included in the 

 same classification with the living plants 

 it will be difficult in many cases to estab- 

 lish perceptible demarcations between, and 

 preserve intact the living groups. 



As to the appearance of secondary growth 

 and its use as a basis of classification, the 

 author points out that such growth is seen 

 first in the rhizomes, then in the stems, 

 branches, leaves and fructifications respec- 

 tively. Thus the subterranean stems of the 

 living SehnintJiostaehys and Botrydiium show 

 the secondary xylem while the aerial por- 

 tions have the structure of the Cryptograms. 



Lepidodendron Sareourtii ( mentioned in 

 Williamson's paper), L. rhodumnense smd L. 

 esnotense are cited as simple arborescent Ly- 

 copods, the trunks of which are without 

 trace of secondary growth. L. vascidare and 

 L. selaginoides show a secondary xylem 

 cylinder of varying thickness in the stems. 

 The Stigmarice he considers more highly 

 organized than the Sigillariw which, accord- 

 ing to the Brongniartian School, they bore. 

 Diploxylon, regarded by some as a Lepi do- 

 dendroid stage, by others as a Sigillaria, has 

 a thick primary xylem surrounded by a bed 

 of secondary xylem, the latter growth being 

 found in not only the roots and stems, but 

 in the foliar bundles also, as far as the base 

 of the leaf. 



The smooth Sigillarias, differing from Di- 



* Bull. Soc. d'Hist. Nat. d'Autun, VI., 1893, Pp. 

 499-504. 



