1902] BRIEFER ARTICLES 301 
The substitute hydathodes are formed only where trichome clusters 
have given place to colleters, and the cuticle has been elevated and 
then split by mucilage. In their formation the tissue first concerned 
is the parenchyma of the bundle sheath, which enlarges greatly, breaks 
through the overlying tissues, and finally grows out into “ Farblosen 
Haaren, die pinself6rmig auseinander treten.”” The neighboring 
palisade parenchyma may share in this formation. The excretion of 
water is presumed to be, as in normal hydathodes, an active process. 
“Nachdem sie ungefahr eine Woche lang allnachtlich Wasser aus- 
geschieden haben, gehen sie allmahlich zu Grunde.” After their death, 
the leaf “ Lasst auf seiner Unterseite durch Wucherungen der Epider- 
mis und namentlich der darunter befindlichen Wassergewebsschicht 
wahlreiche ein-und mehrzellige Wasserblasen entstehen.” 
» Haberlandt’s argument from these data may be epitomized as 
follows. The substitute hydathodes are real organs, and not accidental 
Sructures, Or purposeless results of injury to the -plant, because they 
_ “curin particular places and are strikingly differentiated (the struc- 
‘aral argument), and get rid of the plant’s excess of water (the physiolog- 
‘al argument). They are ew organs because no similar structure is 
_ 2 0n any part of Conocephalus or any related plant. Natural 
i. cannot have produced them because the occasion for them 
4 ae tbe a nature ; no known natural agent destroys the normal 
y am odes, and they remove all the surplus water at the height of the 
imny season. _ And natural selection would have made the substitute’ 
: in cy ie . = ‘i r 
wz ape zweckmassig gebautes und funktionirendes Organ” 
friiheres Vorbandensein einer rudimentaren 
nably permanent, instead of transitory. Summing up, oar 
