232 MASSACHUSETTS HORTICULTURAL SOCIETY. 



finally succumbed, and were wholly destroyed. The three remain- 

 ing ones were removed before this occurred, to furnish comparison 

 with the more advanced cases. Similarly, seeds were germinated 

 in a pot of sterilized soil, without being artificially infected. 

 These, subjected as nearly as possible to the same external condi- 

 tions, did not show any' signs of the malady. 



The fungus, according to my observation, always attacks the 

 plant through its roots. The hyphiie penetrate into aud lietween 

 the cells of the root, causing a complete breaking down of the 

 tissues. In an advanced case of the disease it is almost impos- 

 sible to make out any cellular structure in the lower part of the 

 stem and root. The dissolution of the cellulose cell wall before 

 the advancing h^^phae is very rapid. The root-hairs and sub-epi- 

 dermal growing parts are first affected, the former drooping and 

 becoming functionless even in regions not immediately attacked. 

 The h3'phj>? extend into the stem, and in some instances I have 

 found the mycelium densely matted in the tissues of the leaves, 

 although this does not usually take place until the plant has fallen 

 to the ground. The vegetative hyphie grow with vei'y great 

 rapidity under favorable conditions. I placed within a Van 

 Tiegham culture cell, a plant which showed only a few filaments in 

 its roots ; in eighteen hours it was thorouglilj' covered and pene- 

 trated by the hyphte without having formed a single oogonium. 

 Twelve hours later, owing, probably, to the exhaustion of the food 

 supply and the removal of some of the moisture, oogonia appeared 

 in great numbers in ever}" part of the plant. This illustrates to 

 what an extent the fungus may spread in a single night, and how 

 quickh" it responds to changes in the conditions of food, tempera- 

 ture, aud moisture. 



The hyphixj of the Pythium are much branched, and mosth^ 

 unsegmented, except in regions where reproductive bodies occur ; 

 at such points one or more septa are formed. [Fig. 1.] They 

 \ary in diameter from i^f^ to 6^* when mature, and are usuallj' 

 dark with densely granular protoplasm. The walls are very thiu 

 in comparison with the lumen, making the hyphiv very fragile. 

 The reproductive bodies are of two kinds, — the oogonia aud 

 antheridia, aud the non-sexual zoosporangia. The oogonia are 



* The Greek letter ju, denotes the unit of microscopical measurement, one-thous- 

 andth of a millimeter, or about one twenty-five thousandth of an inch. [En. 



