In Neottiowdeae, the pollen grains cohere loosely into 
sectile pollinia (first step in specialization); in the ad- 
vanced species, these are composed of microspores which 
are united into tetrads, while in the less evolved mem- 
bers (e.g. Cephalanthera, Aphyllorchis, Lecanorchis, Gal- 
eola, Pogonia, Cleistes, Epistephium, Vanilla, etc.), the 
pollinia are formed by single, either monocolpate, ulcer- 
ate or porate grains. 
In the Ophrydoideae, with granular pollinia (second 
step in specialization) and Kerosphaeroideae, with hard, 
compact pollinia (final step in specialization), the pollinia 
are always composed of tetrads, which, depending on the 
position they occupy — whether along the periphery or 
towards the center—may be one of the five basic types: 
1. tetrahedral; 2. isobilateral; 3. decussate; 4. T-shaped, 
or 5. linear. 
The occurrence of single pollen grains and their aggre- 
gation into pollinia are in accord with the primitive or 
advanced status of the five main groups. 
Discussion 
I have attempted to demonstrate, in the diagram on 
Plate XIII, the correlation of the majority of criteria 
discussed in the foregoing paragraphs. The numbers be- 
neath each name summarize, out of the 16 selected char- 
acteristics, the essential constitution of each group, and 
the numbers along the lines connecting these groups are 
those of characters shared. 
It has previously been stated that the dynamic and 3- 
dimensional structure of nature cannot be projected into 
a 2-dimensional perspective without destroying, or at 
best distorting, its salient features. This statement is 
relevant also to the diagram on Plate XIII. For the 
proper interpretation of this projection, we have to visu- 
alize each group (shaded circles) as a 8-dimensional unit 
[77 ] 
