142 MORPHOLOGY 



observed and commented on by succeeding botanists: first by Malpighi' 

 who judged them to be seeds, he having seen them develop new plants; by 



Fig. 8i. Vertical section of young soralium oi Evernia Jurfuracea 

 var. soralifera Bitter x 60 (after Bitter). 



Micheli^ who however distinguished between the true fruit and those seeds; 

 and by Linnaeus^ who considered them to be the female organs of the 

 plant, the apothecia being, as he then thought, the male organs. Hedwig*, 

 on the other hand, regarded the apothecia as the seed receptacles and the 

 soredia as male bodies. Sprengel's^ statement that they were "a subtile 

 germinating powder mixed with delicate hair-like threads which take the 

 place of seeds" established finally their true function. Wallroth", who was 

 the first really to investigate their structure and their relation to the parent 

 plant, recognized them as of the same type as the " brood-cells " or gonidia; 

 and as the latter, he found, could become free from the thallus and form a 

 green layer on trees, walls, etc., in shady situations, so the soredia also 

 could become free, though for a time they remained attached to the lichen 

 and were covered by a veil, i.e. by the surrounding hyphal filaments. Koer- 

 ber' also gave much careful study to soredia, their nature and function. As 

 propagating organs he found they were of more importance than spores, 

 especially in the larger lichens. 



According to Schwendener', the formation of soredia is due to increased 

 and almost abnormal activity of division in the gonidial cell; the hyphal 

 filament attached to it also becomes active and sends out branches from the 

 cell immediately below the point of contact which force their way between 

 the newly divided gonidia and finally surround them. A soredial " head " 



1 Malpighi, 1686, p. 50, pi. 27, fig. 106. ^ Micheli 1729, pp. 73, 74. ^ Linnaeus 1737, p. "325. 

 * Hedwig 1798. ^ Sprengel 1807, Letter xxili. « Wallroth 1825, I. p. 595. 



' Koerber 1841. ^ Schwendener r86o. 



