MISCELLANEOUS COMPOUNDS 271 



substances, and the presence of raphides (a special form of calcium 

 oxalate crystal). Catechol tannins represent a rather ill-defined group 

 of phenolic substances, including probably the leucoanthocyanins; the 

 mere presence or absence of this class of compounds is of dubious 

 systematic value. Cyanogenetic substances, as noted elsewhere, have 

 practically the same limitations. As the cyanogenetic compounds have 

 already been discussed, there is no need to add anything further be- 

 yond the observation that it is most important to know what sub- 

 class of cyanogen is involved; Gibbs' tests for these compounds do 

 not provide this information. 



Since raphides have not been discussed elsewhere, some con- 

 sideration of Gibbs' application of this criterion is appropriate here. 

 Raphides are but one of many forms of crystals of calcium oxalate. 

 They are recognized as bundles of acicular crystals, sometimes occur- 

 ring in special mucilage-containing cells. Of raphides, Gibbs says that 

 they represent "one of the few directly visible chemicals." However, 

 the significance of raphides lies not merely in the fact that they are 

 calcium oxalate (200 or more families of flowering plants and even 

 algae, fungi, and mosses produce some form of calcium oxalate crystals) 

 but rather that a physiological state exists in the cells leading to the 

 deposition of calcium oxalate in the characteristic form of raphides. 

 This latter point has been emphasized by Pobeguin (1943) in his 

 general review of the occurrence of calcium oxalate crystals among 

 angiosperms. 



Gibbs (1958) has applied evidence from raphide distribution 

 to the question of whether the phylogenetic position of the order 

 Parietales (of Engler and Prantl) is closer to Laurales or to Magno- 

 liales, the latter group being favored by Hutchinson. Gibbs notes first 

 that several families of the Parietales have raphides: Dilleniaceae, 

 Actinidiaceae, Marcgraviaceae, and Theaceae (all of the sub-order 

 Theineae).! Members of the Ranales or Magnoliales (of Hutchinson) 

 do not have raphides, but several families of the Laurales are said to 

 have raphides, for example, Myristicaceae, Hernandiaceae, Gomorteg- 

 aceae, Lauraceae, and Monimiaceae. Gibbs has raised the question as 

 to whether the Dilleniaceae came from the Laurales. 



Despite the importance attributed by Gibbs to criteria such 

 as the presence of catechol tannins, cyanide, and raphides, it is the 

 opinion of the writers that such biochemical characters are of limited 

 value unless more specifically defined chemically. Recently, Shaw and 

 Gibbs (1961) described the Hamamelidaceae as follows: (1) + HCl 



1 Raphides are uncommon in the Theaceae, occurring only in the genera Tetra- 

 merista and Pelliciera, which have been placed at times in the Marcgraviaceae, and the 

 genus Trematanthera which has been placed in the Actinidiaceae (Gibbs, 1958). 



