FLORIN: SYSTEMATICS OF THE GYMNOSPERMS 359 



to the subfamily Zamioideae. These discoveries indicate that true cycads already 

 existed in early mesozoie time, l)ut it is not yet possible to decide which of the 

 two subfamilies is the oldest. B^inally, the genera Ctenis, Pseudoctenis, and 

 DoratophyJlum, of early mesozoie age and exclusively based on leaves, their 

 morphology, and epidermal structure, are probably true cycads. 



According to Schuster (1932), the living cycad genera are end products of 

 evolutionary lines which diverged very early. They cannot be divided into more 

 primitive and more advanced types. Stefanoff (1936), however, adhered to the 

 old view of the primitiveness of Cycas, while Gaussen (1944-1952) considered 

 Zamia more primitive. It appears to be generally agreed that the cycads derive 

 from the paleozoic pteridosperm stock. 



Bennettitales 



Harris (1932-1937, 1941a, 1942-1952), Florin (1933), and others, have de- 

 scribed the epidermal structure of many types of sterile leaves, thereby further- 

 ing the classification of fossil eycadophytes. Stem anatomy was investigated by 

 Chrysler (1932) and Wieland (1934), and the anatomy of bennettitalean roots 

 by Carpenter (1932) and Selling (1944, 1951). 



Zimmermann (1932) proved the organic connection between the hermaphro- 

 dite flower of WilliamsonieUa, the leaves of a NiUsoniopteris, and a certain type 

 of stem (cf. Thomas, 1915). Harris (1944) then showed that the flower of Wil- 

 liamsonieUa possessed a perianth of caducous bracts, that the free microsporo- 

 phylls were pinnately branched, that the pollen was produced in two-valved 

 capsules of the same kind as in Cycadeoidea, and that these two genera should 

 be regarded as being rather closely related. Salmi (1932) discovered a new spe- 

 cies of WiUiamsonia, the female fructifications of which were borne terminally 

 on branches, projecting beyond the armor of leaf bases on a columnar stem with 

 a crown of Ptilopliyllum leaves and long scales. The female flower of Vlielan- 

 diella was investigated by Harris (1932-1937). SturieUa (Krausel, 1948) is a 

 new type of inflorescence made up of small bisexual flowers. W ester sheimia 

 (Krausel, 1949a) is unique by having pinnately branched female inflorescences, 

 the lateral parts of which form strobili with numerous seeds and interseminal 

 scales. Wieland (1934) investigated the bisexual flowers of Raumeria. Schnarf 

 (1937) summarized our knowledge of bennettitalean and other gymnosperm 

 seeds. Harris (1947) pointed out the need for information on the phyllotactic 

 relations of the ovules and interseminal scales as well as their vascular connec- 

 tions, and on the integument of the ovule, in the cycadeoideas. The bennettita- 

 lean fructifications are sometimes called flowers, sometimes inflorescences, de- 

 pending upon the supposed nature and position of the seed-bearing stalks. 

 These are often regarded as of the nature of "leaves," but in Lam's (1952) 

 opinion the bennettites are primarily stachyosporous in the female sex, and 

 in that of Emberger (1944) the gynoecium is a branched axis, and the "flower" 

 an inflorescence. 



Of late years the opinion has been expressed that the pteridosperms, cycads, 

 and bennettites form between them a natural group of high rank, the eycado- 

 phytes, the two latter divisions of wliich may both derive from primitive pteri- 

 dosperms (Schuster, 1932; Arnold, 1948; Gaussen, 1944-1952). 



Pentoxyleae. This Jurassic group was described by Rao (1943), Srivastava 



