295 
and Histogeny of Strychnos. 
to which they belong. They are : Vochysiaceae, Malpighiaceae, 
Olacineae, Combretaceae, Melastomaceae, Salvadoraceae, 
Loganiaceae, Gentianeae, Acanthaceae, and Thymelaeaceae. 
Thus every sub-class of Dicotyledons is represented. To this 
list, as we shall presently see, the Onagraceae, Solanaceae, and 
Goodeniaceae should probably be added, while similar, though 
not identical structures are also found in the roots of Cruciferae 
and of Cucurbitaceae. But though the examples are so 
numerous, only a small minority of the plants in question 
have been investigated any further than was necessary to 
establish the bare existence of the anomalous structure. 
Solereder, who was the first to find interxylary phloem in 
sixteen genera, worked entirely on herbarium material, — a fact 
which he regards as advantageous, on account of the authentic 
naming of the specimens investigated h But accuracy of 
specific determination, desirable as it is, is no compensation 
for inexactness in the anatomical results. The examination 
of histological structure in dry material alone, may afford a 
useful clue to the empirical identification of species, but is 
seldom of any use when developmental questions are involved. 
Solereder’s work is of value from the wide field it covers, and 
is highly suggestive of further research, but his statements as 
to development rest on no satisfactory basis. He defines 
interxylary phloem-groups as ‘ those islands of soft bast in 
the wood, which are locally produced on the inner side by a 
normal cambium belonging to a normal circle of bundles 1 2 .’ 
This statement contains an unwarranted generalization. In 
the few cases in which the development has been traced, 
phloem-islands are in some formed on the inner side, in others 
on the outer side of the cambium. We will shortly describe 
the best investigated instances of each. 
Among the Vochysiaceae the phloem-islands of Erisma 
have been observed and figured by Wille 3 , who says that 
they are formed on the inside of the cambium. His figures, 
1 1. c. p. 7. 2 1. c. p. 32. 
3 Om Stammens og Bladenes Bygning hos Vochysiaceerne, Oversigt K. Dansk. 
Vidensk. Selskabs Forhandl. 1882-3. French resume, p. 14. 
