124 
ous equations containing many unknown quantities, x, y, z-..-. Different 
phases of the natural system viewed from different standpoints are to be 
likened to different equations showing the different relations of the unknown 
quanties ; and the natural relations which we are struggling to demonstrate in 
constructing a natural system are somewhat similar to the values of the un- 
known quantities which satisfy the equations. This metaphor, I think, makes 
sufficiently clear that a natural system should be a dynamic one. 
The characters which ENGLER refers to in §§ 16, 17, 18, and 19”, as those 
denoting the stages of advancement, are all the respective peculiarities of the 
plants and they should certainly be taken into account. 
In § 20” he states that the whorl arrangement of floral elements usually 
occurs in correlation with the inferior ovary or zygomorphy. It is true that 
the more the characters come in linkage, the less dynamic becomes the 
system, which shows the natural relations of the plants compared. Conse- 
in the Centrosperme ; Melastomace in the Myrtiflore ; Lentibulariacese and others in the Tubi- 
floree ; and Plantaginaceze in the Plantaginales. 
SECRETORY CELLS, OF VARIOUS SHAPES, WITH RESINOUS (OILY), LATEX-LIKE OR OfHER CONTENTS, 
are found in the following families respectively: Calycanthacze and others in the Ranales ; 
Papaveracee and others in the Rheeadales; Bixacee in the Parietales ; Polygalacee ard others 
in the Geraniales; Sapindacez and others in the Sapindales ; Leguminse and others in the 
Rosales; Myrtacere and others in the Myrtiflore; Cornacee in the Umbelliflore; Rubiacer 
and others in the Rubiales ; Composite and others in the Campanulate ; Plumbaginacee in the 
Plumbaginales; Primulacese and others in the Primulales; Apocynacee and others in the 
Contorte ; Convolvulaceze and others in the Tubiflore; Aristolochiacee in the Aristolochiales ; 
Piperacee and others in the Piperales; Myristicacee and others in the Ranales; Euphorbiacee 
and others in the Geraniales; and Moracee in the Urticales. 
ELoNncatep sEcRETORY sacs are found in the Trochodendracer and others in the Ranales; 
Anncardiacee in the Sapindales; Crassulacee and others in the Rosales; Passifloracew in the 
Parietales ; Rubiaceze and others in the Rubiales; Composite and others in the Campanulatie ; 
Polygonaceve in the Polygonales ; Myristicacew in the Ranales ; and Euphorbiacee in the Geraniales. 
TANNIN-IDIOBLASTS are found in the Violaces and others in the Parietales; Geraniacee in the 
Geraniales; Rhamnacee and others in the Rhamnales ; Leguminosz in the Rosales ; Melastomacez ; 
in the Myrtiflore; Rubiace in the Rubiales; Pirolacee in the Ericales; Gentianacew in the 
Contorte ; Solanace and others in the Tubiflore; Polygonacee in the Polygonales; Aristolo- 
chiaceze in the Aristolochiales; Piperace in the Piperales; Euphorbiacee in the Geraniales ; 
Moraceze in the Urticales; and Ceratophyllacee in the Ranales. 
InrraxyLany PHLo#« is found in the following families: Vochysiacese in Geraniales; Combretacex, 
Myrtaceze, Melastomatacee and others in the Myrtiflore ; Cucurbitaceze in the Cucurbitales ; Apocy- 
nace and others in the Contortz; Convolvulacee and others in the Tubiflore ; Basellacez in 
the Centrosperme ; Polygonaceze in the Polygonales; and Euphorbiacee in the Geraniales. 
1) Enerer, A.—1. c. pp. XIV. XV. 2) Eseuer, A.— Le. p. XV. 
