30 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
hyphe of this young hypothecium arise vertical hyphe, which soon 
become differentiated into paraphyses and asci, appearing first over 
the central portions of the mass of hyph and extending laterally in 
all directions as the hypothecium spreads out by lateral growth. The 
paraphyses and the asci are very similar in their early development, 
but the hyphe which produce the asci very soon begin to enlarge so 
that the asci may be distinguished from the paraphyses while still 
very small. Also these asci-producing hyphe always remain one- 
celled and are much richer in protoplasm than the others. Observers 
have thought that the asci and paraphyses arise from different sys- 
tems of hyphe and have called the supposed asci-producing elements 
ascogenous hyphe, regarding them as arising from ascogonia. But 
more recently Sturgis, in this country, has arrived at the conclusion 
that both asci and paraphyses arise from the same system of hyphe. 
More investigation is needed at this point. As the development pro- 
ceeds the hypothecium is produced into the excipleor the perithecium, 
as the case may be. 
Beginning its development within the thallus, the apothecium may 
remain immersed or it may become more or less superficial, being 
supported in the ways already described. As the apothecium pushes 
upward the surrounding thallus may or not grow up about it to form 
the thalloid exciple, and now, if at all, is formed the epithecium. 
REPRODUCTION. 
SOREDIA. 
Among the means of reproduction in lichens soredia play an impor- 
tant part. These masses of fungal hyphe and alge may in proper envi- 
ronment preduce a lichen thallus. They occur on many foliose and 
fruticose lichens and on some crustose species. A whole soredium or a 
portion of one is easily carried by the wind, and resting on a favorable 
substratum may develop into a lichen thallus having the same struc- 
ture and bearing the same kind of apothecia, soredia, spermagonia, 
ete., as that on which the soredium developed. 
There is no differentiation into layers in the soredium, nor is dorsi- 
ventrality established until after it begins to grow on the substratum. 
As growth begins, the hyphal rhizoids penetrate the substratum to 
secure nourishment and to anchor the minute mass of tissue. As 
growth proceeds, the fungal portion of the soredium usually becomes 
differentiated into cortex and medulla, and the alge come to occupy 
their proper place in the thallus. 
Soredia may develop on the thallus on which they are produced, 
into the isidioid branchlets frequently found on the thalli of some of 
the foliose lichens. Doubtless the reproduction by soredia is the 
most important method in many lichens. Indeed, a considerable 
