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Facts relating to the Structure of Seedlings . 
5. Tetrarchy appears to be characteristic of large seedlings and 
diarchy of smaller ones. For example, in the Cactaceae, Pereskia , 
Nopalea> and Opuntia have typically a tetrarch root, whilst Rhipsalis , 
Echinocereus , Echinopsis , and Mamillaria have a diarch root. 
Following is an analysis of some of the pairs of seedlings raised from 
seeds of closely related plants, which seeds were selected in order that the 
units of each pair might differ, as far as possible, in size. 
In this analysis the following are the abbreviations used : 
3rd column : 1 m. = 1 non-bifurcated main strand, 
1 m. b. = 1 bifurcated main strand, 
2 1. or 3 1. = 2 or 3 lateral strands. 
4th, 5th columns : c. s. = cross-section. 
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