THALLOPHYTES 



Fig. 2. — A group of spo- 

 rangia of Stemonitis, arising 

 from a plasmodium on a frag- 

 ment of wood, showing the 

 slender stalks and linear 

 spore cases. 



Reproduction. — At the time of spore formation, the plasmodium 

 comes to the surface of its substratum, sometimes climbing along vari- 

 ous supports, and then locomotion ceases. The whole plasmodium 

 then forms a single stalked sporangium (spore 

 case); or it organizes several regions, each of 

 which produces a sporangium, the sporangia 

 often forming a close cluster (tig. 2). In 

 sporangium formation the pulsating advance 

 of the protoplasm has been observed, forming 

 the hollow stalk and finally the terminal spore 

 case, whose wall hardens into a firm sheath. 

 Nothing is left of the unused plasmodium 

 except a network of tough strands. The 

 spore case is exceedingly variable in form 

 and general appearance, and often within it 

 there is organized a network of tubes known 

 as the capillitium. In the meshes of this 

 network countless spores are formed, with 

 cellulose walls, most characteristic reproductive cells of plants. The 

 wall of the spore case dries and ruptures, and the hygroscopic capilli- 

 tium expands, often carrying up and exposing the spores to dispersal. 



The structure of the sporangium is not always so complicated as the one de- 

 scribed, for sometimes there is no capillitium, and sometimes there is no stalk. 

 Even the spore case may be lacking, the spores being cut off from branches sent 

 out from the stalk. A still greater modification in spore formation is exhibited 

 in such forms as the common flowers of tan (Fuligo), in which no distinct spo- 

 rangia are seen, but the whole plasmodium and sometimes several blended Plas- 

 modia become transformed into a cushion-like or cakelike mass, known as the 

 aethalium. Within the aethalium the spores are found in irregular chambers, 

 which may be taken to represent a confused mass of indefinite and blended spo- 

 rangia. 



Life history. — In following the life history from spore to plasmodium 

 great variations are encountered, for at every stage there is exhibited 

 extreme sensitiveness to external conditions. A representative series 

 of stages is as follows: From the spore wall the amoeboid protoplast 

 escapes and soon develops a single cilium or flagellum, by means of 

 which it moves very actively. This ciliated cell has quite the appear- 

 ance of certain low animals in structure as well as in movements, and 

 it multiplies freely by division. Eventually the cilium disappears and 

 the cell becomes amoeba-like again, and in this condition it may mul- 



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