SPOROGONIUM OF PELLIA 237 



nation. The egg of Pellia is retained, after fertili- 

 sation, in the female organ, and germinates in situ, 

 so that the embryo is protected by and can draw 

 food from the thallus. This is the first example we 

 have met with of the protection and feeding of the 

 embryo by the mother organism, a condition which is 

 of great importance, and is carried much further in 

 the higher organisms, both plants and animals. 



Sporogonium. — The embryo of Pellia, and indeed 

 of all the Mosses and Liverworts, does not develop into 

 a completely independent plant, but into a spore-pro- 

 ducing structure called a sporogonium (Fig. 36, spn.), 

 which remains attached to the thallus; and the spores 

 produced by this germinate to produce new Pellia plants. 



The mature sporogonium produced from the fertilised 

 egg consists of (i) a foot embedded in and drawing 

 organic food from the thallus, (2) a long stalk, and 

 (3) a spherical head or spore capsule which is at first 

 green. The stalk remains short for some two or three 

 months in the spring while the spores develop, but 

 when these are nearly ripe it quickly lengthens 

 (Fig. 36, A), and in two or three days attains a length 

 of 2 to 3 inches. The spore capsule is now dark, almost 

 black, and in dry air it opens, four splits running down 

 from the centre of its upper surface to the base where 

 it joins the stalk. The four strips of wall thus 

 separated fold back as four separate flaps, which form 

 a cross-shaped structure standing out from the top 

 of the stalk and exposing the mass of spores within 

 (Fig. 36, A). If the opened capsule be examined with 

 a hand lens there can be seen, interspersed with the 

 dust-like spores, a number of delicate threads, the 

 so-called elaters (Fig. 36, B, el.). These are long cells 

 with spirally wound thickenings inside their walls 



