11)8 MASSACHUSETTS HORTICULTURAL SOCIETY. 



ring surrouuding the outer edge is called an aunulus. The sudden 

 contraction of this aunulus ruptures the ripened sporangium, 

 causing it to split open, when the spores escape, as seen in figure 3 ; 

 figure 4, spores. 



In Part 3, plate IV, figures 1, 2 and 3 show the appearance of 

 a spore shortly after germination. Here we have the protruding 

 spore-sac which continues to grow in the manner previously de- 

 scribed, until a prothallium is formed, as seen in figure 4. Figure 

 5, shows to us the young fern just starting on its life's work. 



We have now seen the ultimate results of spore germination, and 

 you have, no doubt, already discovered a partial reason why ferns 

 do not increase more largely by means of spores. For while every 

 spore may produce a prothallium, all prothallia will not produce 

 ferns. A very large proportion prove abortive and perish. Others, 

 being dioecious in character, and becoming separated, or being 

 developed at different times, fail to complete their work. Even 

 mona^cious prothallia are subject to so many accidents that only an 

 exceedingW small proportion of them ever succeed in consummating 

 the purpose for which they were designed. 



Nature has, however, endowed them with some remarkable prop- 

 erties by which destructive agencies are sometimes counteracted. 

 Smith states that a prothallium may be divided into two or four 

 parts, and each part will produce a plant bud, while Dr. Farlow 

 has shown that prothallia sometimes produce fern plants by a pecu- 

 liar process of budding Avithout the aid of reproductive organs. 



I pass over, as too intricate for demonstration here, the elabora- 

 tion of reproductive organs on the prothallium, and the subsequent 

 evolution of the young fern, and for its further elucidation refer 

 you to the standard text books previously mentioned. There is 

 also a very careful and elaborate paper by Henfrey, in A"ol. XXI 

 of the "Transactions of the Linnean Society," page 117, which 

 may be advantageously consulted. 



Hofmeister states that the young plant bears no resemblance at 

 first to a fern and only gradually develops its real character. He 

 also states as a remarkable fact in the life-history of a fern, that 

 wliereas the young fern will produce as many as a dozen fronds 

 during the first year of its existence, after it has reached maturity 

 only a single frond will l)e produced annually, and that a period of 

 four seasons' growth is necessary for the full development of that 

 frond. 



