6 WEISS, The Parichnos in the Lepidodendracece. 



the curious strands of parenchymatous cells running- 

 through the awn of the barley, and which, according to 

 Mikosch ('92), are concerned in increasing the evaporation 

 of water. Such a function might be quite in consonance 

 with the actual structure of the parichnos tissue, but it 

 would not explain the continuation of this tissue into that 

 of the lacunar middle cortex of the stem. One would 

 expect a tissue concerned in transpiratory processes to be 

 definitely connected with the vascular tissue of the leaf 

 base, as the mesophyll of the leaf is through the inter- 

 mediary of the transfusion cells. But of such connection 

 there is no sign in any of the Lepidodendraceae, the 

 parichnos running on the outer or phloem side of the leaf 

 trace. Moreover, there seems no reason in the case of 

 the vegetative leaves to make special provision for 

 facilitating the transpiration, when one remembers the 

 xerophytic nature of the leaves of Lepidodendron and 

 particularly of Sigillaria. In both cases the stomata are 

 sunk in narrow grooves, such as one finds in recent plants 

 requiring to reduce the evaporation of moisture from their 

 leaves. Special transpiratory strands would be in direct 

 opposition to the whole structure of the leaf. 



Dr. Scott (:oo) considers the function of the parichnos 

 strands somewhat problematical (p. 145), but believes that 

 while it is highly probable that they were in part secretory, 

 " the persistence and enlargement of the parichnos on 

 the surface of old stems suggests a respiratory function 

 like that of lenticels " (p. 202). With this latter view I 

 agree entirely. 



The parichnos strand, connecting as it does the delicate 

 and lacunar tissue of the mid-cortex with the intercellular 

 spaces of the leaf, and consequently through the inter- 

 mediary of the stomata, which are found in the longitudinal 

 grooves of the Lepidodendroid leaf, with the surrounding- 



