LYCOPODIUM 145 



air sjmces, the distribution of gree7i tissue, the rigid tissue 



around the outside, the small fibro-vascular handles. kSIiow 



these structures in an outline sketch. 



1. The detailed structure of the stem is complicated and highly 

 specialized for its work of photosynthesis under severe xerophytic 

 conditions. There are many interesting adaptations to these eco- 

 logical relations, as shown by the position of the stomata protected 

 within the lengthwise grooves, the heavy layers of thick-walled tis- 

 sue outside of the green tissue, etc. The study of these adaptations 

 is veiy interesting, but rather special, requiring well-cut sections. 



E. The growing points of stems and roots. These are occupied by remark- 

 able, large apical cells whose structure and activities are best studied 

 by means of microtome sections. They are among the best illustrations 

 of growth from apical cells. 



F. The gametophytes. These can be obtained only by sowing spores when 

 very fresh. The prothallia are irregularly lobed and the antheridia 

 and archegonia are generally developed on separate plants (see Prin- 

 ciples, Fig. 285). 



References. Campbell, 23; Goebel, 16. 



Questions. What are the structural characters of the horse- 

 tails especially adaptive to severe conditions of heat and 

 drought (xerophytic conditions) ? Where is the work of 

 photosynthesis performed ? Have the leaves anything to 

 do with it ? Have the leaves any very obvious functions ? 

 Why are they present especially on the underground root- 

 stock ? What is the form and structure (morphology) of 

 the cone ? What are some of the advantages of the elaters 

 on the spores ? What are the advantages in the spores 

 clinging together so that they germinate in groups ? 



THE CLUB MOSSES, OR LYCOPODINE^ 



134. Lycopodium, the lycopod, or club moss. Species of Lycopodium with 

 well-differentiated cones, such as L. annotinum, L. complanatuin, L. clava- 

 tum, etc., furnish the best material for type studies. Observe when possible 

 the life habits, noting the creeping stems from which arise the upright 

 branches bearinji cones. 



