RANALES 407 



anthers with broad and protruding connectives, which are transformed, 

 distally, into food bodies; staminodes above the stamens; polHnation by 

 beetles; no nectaries; a decurrent stigma; a unilacunar, two-trace node; 

 a many-celled archesporium. 



In contrast with these many primitive characters, are the reduction 

 of the carpel to achenelike structure, with one or two ovules; seeds 

 with a large embryo and no endosperm; vessels with simple perfora- 

 tions; sieve tubes of high type. The concave receptacle, specialized over 

 the primitive, is doubtless also an advanced character, a step in the 

 structural protection of the ovules; it may represent an adaptation 

 to beetle pollination. (The primitive Eiipomatia has a similar concave 

 receptacle. ) The presence of a cortical vascular system is probably also 

 an advanced character. Primitive characters in this family surpass in 

 importance and number the advanced characters; the Calycanthaceae 

 are surely ranalian. 



The placing of the Calycanthaceae in or near the Rosales or Myrtales 

 is not supported by pollen characters or by wood structure. When all 

 characters are considered, the Calycanthaceae most closely resemble 

 the Eupomatiaceae, Magnoliaceae, and Annonaceae. 



Trochodendraceae and Tetracentraceae 



The Trochodendraceae and Tetracentraceae, primitive, unigeneric 

 families, are closely alike in several characters and unlike all other 

 families in the Ranales. They are ranalian in their simple bisexual 

 flowers and vesselless wood. The gynoecium, of several to many carpels 

 in Trochodendron and four in Tetracentron, is syncarpous by the lateral 

 union of the short carpels of unusual follicular type. In Trochodendron, 

 there is further fusion in the adnation of the stamens to the backs of 

 the carpels, an unusual type of perigyny. The form of the anatropous 

 ovule has been called unique in angiosperms. (As the ovules mature, 

 the chalazal region elongates greatly and forms a prominent basal 

 appendage, with a "doubled-back" vascular bundle.) Another unique 

 character in these two families is the structure of the parenchyma of 

 the secondary wood. In gymnosperms and angiosperms generally, uni- 

 seriate wood-parenchyma cells are formed by ti-ansverse divisions of 

 the fusiform xylem initials. In Trochodendron and Tetracentron, the 

 transverse divisions are oblique, rather than at right angles to the 

 long axis of the fusiform cell. 



Taxonomically, the Trochodendraceae and Tetracentraceae have been 

 variously treated. The placing of the Tetracentraceae in the Hamameli- 

 dales disregards its close similarity to the Trochodendraceae in ovule 

 form and in vesselless wood, which has wood parenchyma with unique 

 ontogeny. When all characters are considered, the two families seem to 



