1960] 



MORPHOLOGY AND RELATIONSHIPS OF MOMMA 



characteristics, depends upon the taxa in question. In certain groups it may be 

 important only in characterizing subfamilies, in other groups it may be impor- 

 tant at the family level, and it is entirely possible that it may have little or no 

 taxonomie importance whatsoever. It seems to the authors, therefore, too restric- 

 tive to exclude Diomma from Rutaecae on the basis of a single characteristic 

 when so many other features of the genus indicate its rutaceous nature. 



The occurrence of secretory elements in the leaves of Diomma points to a 

 union with Rutaecae. Blenk (1884) was among the first to report the occurrence 

 of secretory cells in leaves of Rutaeeae. namely in Spathelia simplex L.. consid- 

 ered in Simaraubaeeae at that time. About 20 years later. Schulze (1902) men- 

 tioned secretory cells in leaves of Zantlioxylum fagara L. Neither Solereder 

 (1908) nor Metcalfe and Chalk (1950) mention the occurrence of these cells in 

 leaves of Rutaecae except for Solereder 's citation of Schulze 's work. 



The secretory structures that are obvious when one examines leaves of 

 Rutaeeae are secretory cavities; secretory cells are visible only with the aid of 

 the compound microscope. Engler (1931) states that the secretory cavities that 

 occur in Rutaeeae serve to distinguish this family from the closely related 

 Simaroubaceae and Meliaeeae. The authors would like to suggest that the occur- 

 rence and distribution of secretory cells and their relationship to secretory 

 cavities within Rutaeeae may be of considerable taxonomie importance. 



Although in our study we have been able to examine relatively few speci- 

 mens, statistically speaking, several observations are perhaps worthy of note: 

 I 1) The presence of secretory cells in the leaves of Diomma serves to distinguish 

 this genus from Sohnreyia. In this regard, the occurrence of secretory cells 

 seems to be of generic significance. (2) The distribution of secretory cavities, 

 on the other hand, may be of specific value, at least in Diomma. In the "Diom- 

 ma ulei distribution," secretory cavities are confined for the most part to the 

 margins of leaflets; in the "Diomma fruticosa distribution." secretory cavities 

 are dispersed throughout the mesophyll of the leaflet. 



Xylem anatomy in Diomma resembles that of many rutaceous species. The 

 presence of pore chains and abundant radial pore multiples, in particular, is 

 characteristic of a number of Rutaeeae. Furthermore, woods of Rutaecae as a 

 whole are relatively consistent in their wood structure with respect to the occur- 

 rence of diffuse porosity, simple perforation plates in the vessels, alternate inter- 

 vascular pitting, axial parenchyma which in many cases is scanty paratracheal 

 with or without terminal or non-terminal bands, and non-septate fibers with 

 simple or narrowly bordered pit-pairs (Heimsch 1942) 



Pollen morphology of Diomma does not contradict its placement in Rutaeeae. 

 A preliminary report of investigations (G. Erdtman, in correspondence) indi- 

 cates that "The pollen grains in Sohnreyia exeelsa, in Diomma sp. and Spathelia 

 subintegra (as well as in S. eubensis) have certain characteristics in common 

 with those of Dietyoloma and in Evodia duicllia (possibly also with those in 

 Chloroxylon and Chorilacna) . " 



The condition of monocarpy. that is. where death of the plant follows flower- 

 ing and fruiting, has been reported in Rutaecae, especially in the genera Sohn- 

 reyia (Ducke 1930; Krause 1921) and Spathelia ( Marie- Victoria 1948; Fawcett 

 & Rendle 1920; AYilson 1911). As far as the present authors are aware, this 

 condition does not obtain in Simaroubaeeae. At this point it might be of impor- 

 tance to note that data on the occurrence of monocarpy among dicotyledons 



