STRUCTURE.] THEY HAVE NO SEEDS. 89 



speculation ; for what botanist would think of pronouncing 

 true seeds to be pollen grains ? 



Even Mr. Griffith, in attempting to show an analogy 

 between spores and seeds, does not pretend to make out any 

 identity between them ; and his whole account is that of a 

 growing point, a focus of vitality, and not a seed. 



One cannot but wonder that so clever a man should not 

 have perceived how entirely the following criticism upon his 

 brother botanists applied to himself. 



" The terms used in most of the characters are in several 

 instances unintelligible, as generally is the case when a name 

 is made to pass for an explanation, or when the application of 

 a name is founded on mistaken ideas of the nature or analo- 

 gies of certain parts. In the late work on Genera by 

 M. Endlicher, I find the terms indusium, calyptra, and colu- 

 mella, all in use. And in a note, other general analogies are 

 so extended as to refer one of the organs to the type of a 

 f flos monadelphus ovario infero/ Now of the terms above 

 cited, there appears to me only one (calyptra,) capable of 

 legitimate application, but only as far as regards mechanical 

 function. The difference otherwise is very great; for in 

 Azolla the calyptra is nothing more than what is presented 

 by every dehiscentia circumscissa of a fruit, and is limited to 

 one only of the capsules ; while in Mosses and all calyptrate 

 Hepaticse, it is the pistillum displaced from its base at a 

 remarkably early period. A more real analogy of this part 

 in Azolla is to be found, perhaps, in the seed of Lemnaceae 

 during germination. The term indusium is applied to the 

 capsule itself, whereas, correctly speaking, it is only applicable 

 to a covering of capsules, of a partial or general nature, derived 

 from the surface of the foliaceous body or frond, on which the 

 capsules are situated. This term indusium, which should be 

 distinguished from involucrum, is at most only applicable to 

 Azolla. A columella is the remains of an originally continuous, 

 solid, cellular tissue, unaffected during the development of 

 the spores ; it is a continuation either of a partial or a special 

 axis. It may, I believe, be justly considered analogous to the 

 connectivum of a bilocular anther, or the cellular tissue 

 between the cavities of a plurilocular anther. In Azolla it 



