GROWTH OF PARASITIC FUNGI. 



with oil in germs of fungi, and thus destroy them. In old nurseries, having a tenacious 

 soil, and where healthy pear seedlings cannot now be raised, it may be well to try the ef- 

 fect of paring and burning the surface soil where the pear seeds are intended to be sown. 

 If the burning is so managed as only to char the organic matter, the soil might be freed 

 from the germs of fungi, and its productive powers at the same time increased. 



It is doubtful, however, whether these precautions will in all cases insure the safety of 

 a crop. The spores of fungi are probably admitted into the interior of plants, by the 

 stomata or breathing pores of the leaves, as well as by the roots. Leaves inhale gases 

 and absorb moisture; and how very minute must be the reproductive germs of a plant, 

 when the plant itself, in many Instances, is so small as only to be seen distinctly by the 

 aid of the highest powers of the microscope. If they are admitted into plants by this 

 means, then it is an important question to determine what are the conditions required for 

 their development, and whether any of them are under our control, and by what means 

 they can be avoided. We shall have the surest ground for hoping successfully to subdue 

 this evil, if we can only discover the secret of its power. I think it may be assumed that 

 fungi have not the power to destroy healthy vegetation — if they had, where would be the 

 limit of their ravages.'' The Rev'd. M. J. Berkeley, who is highly distinguished for his 

 knowledge of fungi, has observed young plants of Botrytis infestans springing from with- 

 in the cells of a potato. As the potato tuber is considered to be formed exclusively 

 of matter which has been prepared by mature leaves, these germs could not have immedi- 

 ately vegetated on entering the potato plant, but were probably carried with the elabora- 

 ted sap of the leaves, and deposited with it in the tissue of the tuber. Mr. Berkely has 

 further stated that " it seemed to him most certain, from observation of those fungi which 

 grow from the tissues of plants, that minute particles, too small to be distinguished by the 

 highest powers of the microscope, must be carried about with the juices, and when fitting 

 circumstances concur, proceed to act on the tissue with which they are in contact." What 

 then are these fitting circumstances.'' The two tribes into which fungi may be artificially 

 divided, have separate tasks assigned to them. The office of one is obviously to hasten 

 the decay of matter which is already decaying; the office of the other, I believe, is to 

 prey upon or hasten the death of that which is unhealthy. Those which flourish on dead 

 organic matter, appear only when decay has commenced, not while it is yet fresh — a fact 

 well known to many. " Fungi," says Mr. Soil}', " are only developed in those solutions 

 which are in that state of putrefaction favorable to their growth; moreover, they do not 

 appear till the solution has acquired that state." There must, I believe, be unhealthy 

 action, possibly some slight chemical change in the fluids of superior plants, before parasi- 

 tic fungi can successfully attack and destroy them. Mr. Berkeley, however, whose opinion 

 i,s entitled to much deference, considers that the growth, and especially the numbers of 

 fungi, depend upon certain atmospheric influences. There can be no doubt, whatever, 

 that the state of the weather has considerable influence on the development and increase 

 of fungi in ordinary cases. For instance, in moist, dull seasons, crops are observed to be 

 alwa3's more or less affected by mildew. Any sudden check in the progress of vegetation, 

 such as is caused when hot sunny weather is succeeded by calm dull days, or by a sudden 

 transition from weather favorable to rapid growth, to weather cold and wet, is generally 

 considered the precursor of blight, and favorable to the growth of fungi. Now, circum- 

 stances like these would exercise an injurious influence on the health of the larger plants; 

 it is therefore doubtful, whether it is not the state of the plant attacked, rather than any 

 peculiar atmospheric condition which favors the growth of the parasite 



Other facts seem to indicate very clearly that circumstances of soil, situation, manure, 



