16 



or globose, largest in species with very large spores, or with those 

 having very numerous spores in the Theke. 



The Spores. 



The Spores, the germinating organs of the Lichen, demand partic- 

 ular attention. To obtain a better view of them the thin section of 

 the Apothecium may be crushed with the linife and spread out as 

 thinly as possible, or one may take off a portion of the upper part 

 of the apothecium, with as little as possible of the surrounding parts, 

 or when the Apothecia are small one or more may be taken entire 

 and crushed in the same manner. In the case of the Apothecia of 

 the fifth Tribe, which have a hard and horny perithecium, this may 

 be lightly crushed, when the nucleus can usually be detected by a 

 lens and separated with the point of the knife. But it is desirable 

 to make sections of Apothecia of all the Tribes, so as to study the 

 structure as a whole. Most Apothecia will stand a good deal of 

 crushing ; but in species with very large spores some care is requi- 

 site to avoid crushing the spores thernselves. In every species the 

 observer should seek to see the spores in the thekes, so as to be sure 

 of their character and number. Otherwise he will be liable to mis- 

 take other cells which may be mixed in the preparation, for spores. 

 In the case of the Pertusarias, in which the Thekes are colored blue 

 by iodine, and are conspicuous under the lens, it is well after a slight 

 crushing to apply the iodine, thus rendering them visible, when they 

 can be separated with the point of the knife from the other parts. 

 Two re-agents are useful in this part of the study : (1) a phial of 

 liquor potassa, which to a certain degree dissolves the hymenial gel- 

 atine and renders the hymenium more easily separable ; (2) a solu- 

 tion of iodine, of which the formula is iodine 1 grain, iodide of po- 

 tassium 3 grains, pure water 1 ounce. As liquor potassa is caustic 

 and poisonous it must be handled with care. The best mode of appli- 

 cation is after the preparation is placed in water under the covering 

 glass, to press with the finger on one edge of the glass, then to place 

 a drop of the solution against the opposite edge, and raise it slightly 

 with the point of the knife, when the solution will flow under. For 

 softening the hymenium with aqua potassa it may be soaked for 

 some minutes in a fifty per cent, dilution of it. The effect of iodine 

 is to color the hymenium, and sometimes the spores, blue, violet, or 

 various shades of red. This color is removed by the addition of a 



