1902] BRIEFER ARTICLES 305 
opportunity ; to some extent the intercellular spaces become charged. 
In Atkinson’s experiments the plants became wet; it probably did 
_ not occur to him to look for the extrusion of water from the sounder 
oedemata. In our experiments, instituted to see if this took place, 
the oedemata merely became wet when evaporation was prevented ; 
drops of water were not excreted by them, however freely they might 
be forced out along the margin of the leaf. Evidently, though water 
_ tan be forced through them, they are passive in the process, and the 
water escapes the easier way. But Atkinson says that water is set free 
by the collapse of hypertrophied cells: ‘The changes brought about 
by the escape of water from this and adjacent tissues during the 
"ammer parts of the day may be so profound as to cause the leaf to wilt 
and die.” 
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On the tomato then we have the same abnormal condition which 
“aused the formation of the substitutes hydathodes of Conocephalus, 
‘Producing Structures which are like them in being formed on the 
: veins, and in being formed from a group of cells of various tissues, 
‘Which become tubular and segment below, and swell up at the free 
. me without doubt there are other details of resemblance—as in the 
Sewell and Scanty protoplasm. Unquestionably, the two structures 
< te homologous ; but on the tomato the oedemata excrete little water, 
- tthe loss injures the plant. Their appearance is a pathological phe- — 
tenon, whose cause is clear ; to seek to discover a purpose forthem > 
: be fatuous. Natural selection has provided the plant with = 
ponses to many frequently recurring pathological conditions. The oe 
raat Conocephalus were always liable to mechanical injuries; = 
: agp whose wounds healed had in such cases an advantage oo : 
ey, utting off of the substitute hydathodes by a callus may be 
at < hatural selection. But such exigencies as the loss of the 
> Must have occurred to Conocephalus practically as rarely 
oe ve Sublimate entered them. Of course, natural selection IS 
_ 2 for the results. On grounds that we cannot yet eee 
chlin... ou = theory, the hydathode responds to the corrosiv€ = 
* Py dying, and the leaf responds to the excess of water by the oe 
"Pay Of groups of cells. The relation of cause and effect $0 
: clear, the details equally mysterious, in the two cases. We e 
nits of 10 eh in both or neither. If the “ Ersatz-Hydathode : . 
Niger. Uction as evidence of the reign of an “ Entwicklungs” 
tts... the fatal action of corrosive sublimate must make us sus- 
““Sence of a power of evil. es 
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