n6 PLANT PHYSIOLOGY 



Nutritive Solutions. Of these a considerable number have been 

 recommended, all no doubt good, since the combinations matter little so 

 long as the necessary substances and quantities are present. I have found 

 that given by Detmer, 2, practically one of Knop's, to be admirable for all 

 ordinary uses. It consists of 1 g. calcium nitrate and .25 g. each of potassium 

 chloride, potassium phosphate, and magnesium sulphate, all dissolved in 

 a liter of distilled water to which is added a few drops. of ferric chloride. 

 The solution without nitrogen is made up in the same way except that cal- 

 cium sulphate replaces the calcium nitrate. Doubtless it would be better, 

 in order to prevent the development of organisms in the solution while stored, 

 to dissolve the salts in 50 cc. of distilled water, and dilute as needed. For 

 other solutions and various accessory matters, consult Detmer, i, or Dar- 

 win and Acton, 58. 



Culture minerals put up compressed in tablets, said to be very convenient 

 in use, have been introduced by Edward F. Bigelow of Stamford, Conn., 

 from whom they may be obtained at a low price. He has described their 

 use in the Nature Study Review, 1, 1905, 69. 



Water-culture Vessels. For the most efficient work with water- 

 culture, very large vessels, and a number of special precautions, are neces- 

 sary, upon which full information may be found in the works of Detmer 

 and of Darwin and Acton, above cited. For our present purpose, how- 

 ever, and for most simple demonstrations, where the plants are not to be 

 carried through a complete cycle back to the seed, very much simpler arrange- 

 ments are ample. Thus small wide-mouth bottles, covered with black paper 

 and fitted with corks cleft at the margin to hold the seedlings, are used with 

 success in the United States Department of Agriculture, where also a sys- 

 tem has been developed'of germinating the seedlings upon paraffined or gutta- 

 percha netting supported by corks on water (Livingston, The Plant 

 World, 9, 1906, 11, and later information). I have, however, found the 

 following simple arrangement wholly satisfactory. Take two of the largest 

 procurable plain glass tumblers, and cast for them covers of hard paraffin 

 blackened by admixture of lampblack. This can be done best by use of 

 a mould turned for the purpose from wood, and covered with glycerin to 

 prevent adhesion of the paraffin, though the mould may be extemporized 

 from cardboard, or even dispensed with in favor of the top of the tumbler 

 itself into which the melted paraffin can be poured upon the water, though 

 this is less satisfactory. The cover should be some 5 mm. thick, and have 

 a projecting rim as shown by the accompanying figure (Fig. 29). Holes 

 may now be bored by a hot iron and made of just the size and form to hold 

 the seeds firmly upright. The tumbler is now surrounded by a readily 

 removable shell of opaque paper, which should darken the tumbler, to pre- 

 vent development of Algas. The seeds may most conveniently be germinated 

 in a saucer germinator (described later under Growth), though they will 

 germinate in place on the cover almost equally well if soaked and covered 

 temporarily by wet filter-paper. For our present purpose the seedlings once 

 started need no further attention ; but an occasional change of solution will 

 permit their continued healthful growth. For some plants an occasional 



