Scnecio prcEcox, D. C, from ]\Icxico. 35 



and receptacles from which exude a resinous or balsamic sub- 

 stance. While botanizing in Mexico during- the summer of 

 1896, plants in all stages of growth were gathered and pickled 

 in a barrel containing one per cent formalin.* 



Looking at a cross section of a stem at least an inch and a 

 quarter in diameter, which has been preserved in formalin, one 

 is struck by a small disc-like area in the centre of the pith, a 

 trifle over a quarter of an inch in diameter. In longitudinal 

 section, the depressed circular area is seen to correspond to 

 lens-shaped spaces, between the watery lamellae or discs of 

 pith, one-eighth of an inch or more in thickness (Plate VIII, 

 Fig. 1). The pith cells are large, nearly twice as long as 

 broad, and are filled with water (which is evidently cellular 

 water), because in the formalin material, the protoplasm was 

 found balled in the centre of the cell. The discs of pith are 

 highly turgescent in the living plants (Plate VIII, Fig. i), and 

 a considerable amount of water is thus stored up, whether in 

 combination with a mucilage or an organic acid could not be 

 ascertained. When the pith is pressed the water exudes in 

 small drops. The peculiar translucency of the cells indicates 

 a large liquid content. The wood and medulla are very inti- 

 mately connected together. The cortex can be removed 

 from the stem with ease, leaving the wood and pith closely 

 united. It is extremely hard to sever this connection without 

 tearing the pith. As will become evident when the histology 

 of the stem is presented, a number of the xylem bundles run 

 a considerable distance into the pith, and thus bind the 

 medulla to the woody cylinder. 



* E.xamination of the above mentioned material at this writing, December 24, 

 1897, si.\teen months after collection, shows that all of the plants thus preserved 

 are practically unchanged ; a high encomium to pay a preservative liquid which 

 stood in an open barrel covered by a lid and a cloth for that length of time. 

 Botanists, therefore, who go to the tropics, should carry formalin, in preference to 

 alcohol and the ordinary felt driers, because specimens preserved in formaldehyd 

 can be dried and mounted for herbarium purposes with but slight loss of color 

 upon relurn to civilization. 



