1912] CURRENT LITERATURE 8l 



prenanthoides. The characteristic periodicity curve of mean values in these 

 species rises quickly to a maximum in the early part of the season, after which 

 there is a much more gradual decline until the end of the season. Only in 

 Melampodium divaricatitm and in Cosmos sulfureus was there no essential change 

 throughout the season, the former species having a single mode on 10 with the 

 mean slightly above 10 in every collection made, and the latter species pre- 

 senting a similar constancy, having at all times a half-curve, falling steeply 

 from a strong mode on 5 only to higher values. In most of these species the 

 modes were on the Fibonacci numbers; and while the changes in mean values 

 were gradual and continuous, the appearance of modes on intermediate num- 

 bers was relatively rare. In Anthemis Cotula 11 and 9 appeared as transition 

 modes between 13 and 8; 9 also appeared momentarily in Zinnia Haageana, 

 Z. tenuiflora, and Laya platyglossa; and 11 and 12 in Sanvitalia procumbens. 

 In three heterocarpous species, Dimorphotheca pluvialis, Laya platyglossa, and 

 Sanvitalia procumbens, the plants grown from the two kinds of seeds produced 

 essentially like variation curves. The same thing was true of plants grown in 

 different years and in different environments, the modal numbers and char- 

 acteristic slopes of the periodicity curves remaining unchanged for the par- 

 ticular species, though the mean values were considerably modified. — Geo. 

 H. Shull. 



Roots of Psaronius. — Since the removal of the great mass of the 

 marattiaceous plants of the Paleozoic to the seed plants, more critical attention 

 has been given to Psaronius as the sole evidence of the existence of the Marat- 

 tiaceae at that early period. Among the structures differentiating Psaronius 

 from modern Marattiaceae, the most striking is the difference in the location 

 of the secondary roots in relation to the stem. In the modern representatives 

 of the family these roots bore their way for a considerable distance through the 

 cortex of the stem before they penetrate to the surface. At all points in their 

 course they are sharply marked off from the cortex by remnants of broken- 

 down cells. In Psaronius they form a wide zone in the cortex of the stem in 

 which there are no remnants of leaf traces or leaf scars, and no sharp distinction 

 between the root cortex and the parenchyma in the interstices between the 

 roots. Stenzel's explanation of this root layer as homologous with the outer 

 cortex of the Marattiaceae has passed current without question until the last 

 ten years. In 1902 Farmer and Hill suggested that the parenchyma in the 

 interstices of the roots of Psaronius might be of the nature of hairy outgrowths 

 rather than cortical parenchyma of the stem. 



The question thus raised has been attacked by Solms-Laubach 1 * with 

 convincing results. He worked cheifly with thin sections of fossils (P. H a id in- 

 geri) from Manebach, supplemented by material from the Museum of Rio 



19 Solms-Laubach, H. Grafex zu, Der tiefschwarze Psaronius Haidhtgeri von 

 Manebach in Thuringen. Zeitschr. Bot. 3:721-757. figs 7. 1911. 



