240 BOTANY. 



through all their changes. The spore of a particular species must be 

 sown, and the development of hyphse, mycelium, sporangia, etc., care- 

 fully followed ; and the greatest care must be taken to guard against 

 error from the accidental presence of other species. 



(c) " Pan culture," which consists in sowing the spores upon or in the 

 nutritive medium in pans or deep plates covered by bell-jars, must always 

 be resorted to, even if more accurate cultures are also made. By placing 

 a quantity of horse-dung in a pan under a bell-jar, there will soon be 

 obtained a good supply of vigorous Moulds ; sometimes several speciea 

 may be obtained from a single pan. By care a few sporangia of each 

 species may be obtained from this first culture, with little probability 

 of contamination ^vith other species. These are to be used for more 

 careful cultures. 



(d) If now moistened pieces of fresh bread are placed under a bell- 

 jar, and a few of the spores of a particular species are sown on them, 

 the growth and successive stages of development may be easily fol- 

 lowed. Instead of bread, other materials may be used, as stewed 

 prunes and other fruits, pieces of oranges or lemons, etc., and for cer- 

 tain species the half-cleaned bones of beef from the kitchen. 



(e) Where still greater care is desirable, the nutritive media may be 

 prepared by boiling and filtering, after which they are placed in thor- 

 oughly cleaned pans or plates, and covered by clean bell-jars ; in these 

 are placed pieces of hardened plaster of Paris or earthenware (porous), 

 which have previously been heated so as to destroy all spores, and upon 

 them are sown the selected spores. The sources of error are in this 

 way very much reduced, but it must be borne in mind that they are by 

 no means all eliminated ; hence the student must be constantly on the 

 lookout for other species than the one under culture. 



(/) The media recommended by Van Tieghem and Le Monnier are, 

 (1st) boiled and filtered orange juice, which, being acid and saccharine^ 

 is not so liable to be invaded by other common Moulds ; (3d) a decoc- 

 tion of horse-dung, boiled and filtered ; this is neutral and alkaline, and 

 serves as a medium for many species ; but it is open to the objection 

 that it is liable to the invasion of intruding species ; (3d) a saline solu- 

 tion of the following composition : 



Calcium nitrate 4 parts. 



Potassium phosphate 1 " 



Magnesium sulphate 1 " 



Potassium nitrate 1 " 



Distilled water 700 " 



[Sugar 7 parts.] 



In some cases the sugar may be omitted. 



(gr) The most accurate and satisfactory, but at the same time most 

 difficult cultures, are cell-cultures. These are made as follows : glass, 

 tin, or India-rubber rings four to five millimetres high are fastened to 



