Pomona College Journal op Economic Botany. 



319 



in a hot, humid atmosphere. Each year the |?rowers change the soil in 

 their green-houses so as to secure soil rich in plant food and freer of 

 disease organisms. 



The stem-rot disease, which is due to a species of Fusarium, may make 

 an attack at any time during the life of the plant, hut it is more serious 

 at certain stages in its propagation, that is, at such times when the plant 

 has to submit to rather sharp changes in conditions of moisture or temper- 

 ature, thus weakening its natural vitality. There are three such periods in 

 the life of the plant which are well marked. The first and probably the 

 most critical one comes when the plant is "benched," that is, when it is 

 transplanted from the outdoor beds into the green-house. A few Avarm, 

 cloudy days, on over-moist soil, or too deep settine of the plants are condi- 

 tions which favor the development of stem-rot. The second critical period 

 comes when the steam heat is turned on in the autumn ; again the plants 

 may be subiected to a rather sharp chansre in temperature. The third and 

 last critical period comes in the sprin?, when the temperature gets abnor- 

 mally high and the plant is low in Antality from having been forced during 

 the year in the production of flowers. 



As Mr. L. IVrnnorin has observed, the diseased plants are recognized 

 by the A\nlted. vellowish, dryinsf-up condition of the foliaffe and a softened 

 condition of the stem at the surface of the cround. Tn the early stages of 

 the disease the mots and upper portions of the branches are sound, while 

 the intervenin"' portion will show brown and blackened areas. Fre- 

 quently one or two branches become affected and wilt before the remainder 

 of the plant shows anv sifus of the disease f Plate 1"). However, it even- 

 tually spreads upward and downward until the whole plant is in a more 

 or less advanced statre of decav. The roots become thoroughly decom- 

 posed and rot off: the stem and its branches become dry and brittle, charac- 

 teristic of dry rot. Upon a nlant where the disease is fairlv well advanced, 

 small fle«h- or salmon-colored clusters of spores are often found. A micro- 

 scopical examination of them reveal« the presence of the characteristic 

 curved Fusarium maeroconidia. A similar examination of the tissue of the 

 afl'ected stems .shows the presenco of abundant mycelium in the parenchyma 

 cells, althnuph the upper branches and the roots of the plants are apparentlv 

 in a perfectly healthv condition. The progress of the disease is normally 

 slow, but in an exceptionally warm and moist atmosphere, the disease 

 organism mav destroy tissue very rapidlv. as pointed out bv the descrip- 

 tions rf inoculaieti plants in another part of this paper. It is probable 

 that s^me di«ea«ed plants continue to produce flowers for months after they 

 are infcfted. Growers report that some varieties are more susceptible than 

 others, and the foUowin" kinds have been mentioned bv several a.s being 

 amon'i' the most susceptible : — Enchantress, Prosperity, "Winsor, Perfection, 

 and Nelson Fisher. 



