3i6 



brings disease of blades in its train and only later do para.-itic organisms 

 infest the diseased parts. 



We consider Brizi's experiments as decisive and think that suflfocation 

 of the roots during high temperature, which greatly increases the leaf activ- 

 ity, is the first impulse to the disease. The soil should be aerated at once. 



THK DlSKASKS of (il.ADIOLI. 



A phenomenon of disease, not rare in cultivating gladioli in heavy soils, 

 or on pieces of ground with a lighter soil, but a higher ground water level 

 in wet years, may be traced to a lack of oxygen. The disease manifests 

 itself in the often sudden oeath of the plant at a time when the inflore- 

 scence is already developed. At first the lower leaves seem marbled with 

 yellow (noticeable at first only when the light falls through them). The 

 chlorophyll bodies decompose and leave yellow drops which look like oil. 

 ^Vhile this process advances apparently in stripes between the veins in the 

 aerial parts of the leaves, brown, depressed places are found on the leaf 

 bases still below the soil which initiate a complete decomposition of the leaf 

 parenchyma. No real weakening takes place, but the decomposition repre- 

 sents a process of humification. Bacteria and often also fungi, small worms, 

 mites, etc., are always found in these tissues which smell sour like humic 

 acid. The aerial parts of the leaves dry quickly and become covered with 

 black pits of Cladosporium and Alternaria. 



Despite the wealth of parasitic organisms present, the disease should not 

 be characterized as parasitic, since the first stages, viz., the brown coloring of 

 the ducts and of the parenchyma, lying close to them, are produced 

 within the iiealthy tissue without the co-operation of such organisms. Later 

 a number of the duct tubes are filled with a cloudy, brown mass which be- 

 comes firm like gum. The latter phenomenon has been observed also in 

 other plants, the roots of which were injured by continued moisture in the 

 soil and the lack of oxygen thus produced artificially. 



(iladioli like a great deal of moisture in the soil but it should not be 

 long continued. In dry years the mistake is often made of watering bulbs 

 and tuberous plants every day. This is wrong, the excessive drying of the 

 soil must be prevented by mulching with litter. 



k. Change.s Due to a Lack of Carbon-Dioxid. 



Despite the small content of possibly 0.036 to 0.040 volume per cent, 

 of carbon-dioxid, which the air' possesses, while consisting of nearly 79 

 parts of nitrogen and 21 parts of oxygen, it suffices everywhere for a high 

 rate of growth; if this important nutrient substance is entirely lacking, the 

 other factors of growth are without value, even in a most favorable com- 

 bination, as may be observed experimentally by placing vessels of caustic 



1 According to Jolly's investigations (cit. in Forsch. a. d. Gebifte der Agrikul - 

 turphysik. 1879, p. 325) the oxygen content of the air varies not inconsiderably 

 (between 20.53 and 20.86 per cent.). The largest oxygen content is found with a 

 prevailing polar current and the least with a prevailing equatorial current. 



