FEKNS. 



169 



277.. Germination of the Spores. — After the spores have been 

 sown for about one week to ten days we should mount a few in 

 water for examination with the microscope in order to study the 

 early stages. If germination has begun, we find that here and 

 there "are short slender green threads, in 

 many cases attached to brownish bits, the 

 old walls of the spores. Often one will sow 

 the sporangia along with the spores, and 

 in such cases there may be found a number 

 of spores still within the old sporangium 

 wall that are germinating, when they will 

 appear as in fig. 142. Kig , MO- 



278. Protonema. — These short green , Spo« of Pteris semi- 



lata showing the three- 



threads are called protonemal threads, or rayed elevation along the 



r , , ' side of which the spore 



protonema, which means a first thread, and wail cracks during germi- 

 it here signifies that this short thread only 

 precedes a larger growth of the same object. In figs. 142, 143 

 are shown several stages of germination of different spores. 

 Soon after the short germ tube emerges from the crack in the 

 spore wall, it divides by the formation of a cross-wall, and as it 

 increases in length other cross-walls are formed. 

 But very early in its growth we see that a slender 

 outgrowth takes place from the cell nearest the 

 old spore wall. This slender thread is colorless, 

 and is not divided into cells. It is the first rhiz- 

 oid, and serves both as an organ of attachment 

 for the thread, and for taking up nutriment. 



279. Growth of the prothallium. — Very soon, 

 if the sowing has not been so crowded as to 



Fig. 141. 

 Spore of Aspidi- 



wUh a wTnged hol ex! prevent the young plants from obtaining nutri- 

 ospore. ment sufficient, we will see that the end of this 



protonema is broadening, as shown in fig. 143. This is done 

 ■ by the formation of the cell walls in different directions. It 

 now continues to grow in this way, the end becoming broader 

 and broader, and new rhizoids are formed from the under surface 



