842 REPOKT — 1903. 



b. Cycads, 



One of the most striking features of the Mesozoic vegetation is the abundance 

 and wide distribution of Oycadean plants. To-day the Cycads or Sago-Palms are 

 represented by ten genera and about eighty species ; they are plants which occupy 

 a subordinate position in modern floras, and occur for the most part as solitary 

 types in tropical latitudes, never growing together in sufficiently large numbers to 

 constitute a dominant feature in the vegetation. Cycads have long attracted 

 attention as exhibiting morphological features of considerable interest. During 

 the last few years the work of Ikeno, Webber, and Lang has shown us that the 

 pollen of Cycas, Zamia, Stanyeria, and probably of the other recent genera, pro- 

 duce spirally ciliated motile spermatozoids, the type of male cell previously regarded 

 as constituting one of the well-defined distinctions between the Vascular Crypto- 

 gams and the Seed-bearing plants. The study of Palaeozoic plants has done even 

 more to break down the artificial barrier between Cycads and Vascular Crypto- 

 gams, by demonstrating beyond all reasonable doubt that our modern Cycads 

 represent a small group of survivals descended from ancestors common to them- 

 selves and the ferns. Cycadean plants must have been among the commonest 

 members of Mesozoic floras. Before the end of the Palaeozoic era there existed 

 plants bearing pinnate fronds similar to those of recent species of Cycadacese, and 

 in succeeding ages the group rapidly increased in number and variety till, in the 

 J urassic and the early Cretaceous periods, the Cycads asserted their superiority as 

 the leading type of vegetation. The majority of Mesozoic Cycadean fronds are 

 assigned to artificial or form-genera as an indication of our ignorance of their 

 reproductive organs, or of the anatomical structure of their stems. As Professor 

 Nathorst has recently suggested, it is convenient to speak of these Cycadean 

 remains as belonging to the group Cycadophyta. On the other hand, we find 

 numerous petrified stems bearing well-preserved reproductive organs which enable 

 us to compare the extinct with the existing species. We are in possession of 

 enough facts to justify the statement that the majority of Mesozoic Cycads bore 

 reproductive organs which difiered in important morphological characters from 

 those of existing forms. The researches of Williamson, Carruthers, Solms- 

 Laubach, Lignier, and others, have revealed the existence of a large group of 

 Cycadean plants — known as the Bennettiteje — almost identical in habit with modern 

 sago-palms, but distinguished by the complexity of their reproductive shoots. 

 The Bennettiteae, originally founded on a petrified stem discovered more than 

 fifty years ago in the Isle of Wight, and represented by another fossil which 

 Carruthers made the type of a new genus, Williamsonia, in 1870, possessed a thick 

 stem, clothed with an armour of persistent leaf-bases and bearing a crown of 

 pinnate fronds, as in most modern Cycads ; but their flowers, which were borne 

 on lateral shoots, were more highly specialised than those of the true Cycads. 

 While most of the Mesozoic Cycads were no doubt members of the Bennettiteae, 

 others appear to have possessed reproductive organs like those of recent species. 

 The Bennettiteae belong to that vast army of plants that succumbed in the struggle 

 for existence aeons before the dawn of the Recent period. The other section of the 

 Cycadophyta, the Cycadaceae, still lingers on as one of the select band whose 

 present insignificance constitutes a badge of ancient lineage, and a faint reflection 

 of past supremacy. 



The wealth of Cycadean vegetation during the latter part of the Jurassic and 

 the earlier stages of the Cretaceous periods is admirably illustrated by the dis- 

 covery in the Black Hills of North America, and in other districts of the United 

 States, of hundreds of silicified trunks of Cycadean plants. The first discovery of 

 petrified Cycadean stems in America was made by Tyson in 1859, who found two 

 specimens in the Potomac beds of Maryland ; since then more than 700 trunks, 

 remnants of a vast Cycadean forest, have been obtained from the Black Hills 

 alone. The investigations of Mr. Wieland, of Yale, who has been engaged for 

 some time on the examination of this rich material, have already revealed the fact 

 that in some of the Bennettiteae the male and female organs were borne in a single 

 flower, the female portion having a structure identical with that previously 



