362 PRACTICAL COURSE IN BOTANY 
ing degrees of irregularity, like the coast line on a map. 
The relative positions of the different orders we have 
been considering are represented by upright and diagonal 
lines, the general course of which, as indicated by the 
arrows, is intended to give an idea of the trend of evolu- 
tionary progress in the particular group represented by each 
line. No one of these lines is made to originate directly in 
any other, because, with the possible exception of the mono- 
cotyls, we have no authority for asserting that any such direct 
connection exists between plants as we know them, but only 
that certain types give evidence of descent from a common 
ancestry. This lack of certainty is expressed by placing the 
point of origin for any given line in more or less close proxim- 
ity to the one which is supposed to be the nearest living 
representative of the common ancestor. The line of ferns, 
for instance, is depicted as originating in the region of the 
bryophytes, somewhere in the neighborhood of the liverworts, 
but the two lines nowhere come in contact, because there is 
no evidence that any fern, living or fossil, is directly de- 
scended from any particular kind of liverwort known to us. 
With these explanations, the diagram shows, in a rough way, 
the generally accepted view of plant relationships as based on 
the evidence at present before us. But in questions of this 
sort it is wise to keep in mind the blunt remark of a famous 
old American statesman, that “only fools and dead people 
never change their opinions.” 
Field Work 
1. If you live in the country, study the appearance of plants affected 
with blights, smuts, rusts, and mildews, and learn to recognize the different 
kinds of disease by their signs. Notice which kinds are most prevalent in 
your neighborhood, and what plants are most affected by them. 
2. Notice the different kinds of mushrooms you find growing wild. 
Observe the difference between those that grow on the ground and those 
that grow on‘logs, stumps, and trees; between those found in the woods 
and those in open ground. Find out how those on the ground get their 
nourishment. Uncover the mycelium, and notice the extent of its surface. 
