96 



BOTANY 



There is no difference between vasit'orm tracheides and vessels other than that 

 the former are single elongated cells, and the latter fused cell rows. Generally 

 speaking, tracheides are formed in parts of plants still in process of elongation, 

 vessels in parts where growth in length has already ceased. True vessels make 

 their first appearance in some of the Ferns, for instance, in the common Bracken 

 (Pteris aquilina). In the main, despite the name Vascular Cryptogams, Ferns 

 have only vasiform tracheids. Even in the Gymuosperms the Gnetaceae are the 

 only family regularly provided with vessels. It is in the Angiosperms that vessels 

 first become of frequent occurrence. Vessels are not of an unlimited length. A 

 few plants, however, such as the Oak, and especially climbing woody plants, or 



Km. 104. Tangential section through 

 the periphery of the stem of 

 Scorzonera hispanica, showing re- 

 ticulately united latex vessels. 

 (x 240.) 



Fi<;. 105. Lower third of a scalari- 

 form vessel from the rhizome 

 of the common Bracken KITH. 

 J'ttrif miiiiii mi. t, Transversely 

 elongated pits in the lateral 

 walls ; q, scalari form perforations 

 of the terminal wall. (After DK 

 BABY, x >.>'.) 



Lianes, have vessels several metres long ; but, as a rule, their length is not more 

 than a metre, and in plants the woody portion of which conducts \\ater only by 

 vessels, the vessels have an average length of only ten centimetres. The length of 

 an individual vessel is denned by the presence of transverse walls, which are not 

 perforated but bear bordered pits. 



A similar fusion to that seen above to occur in the formation of 

 laticiferous vessels is also met with in fungal hyphse ; by an absorp- 

 tion of a part of the wall where two branches come into contact, their 

 protoplasmic contents unite. A still more complete fusion is exhibited 

 by the naked amoebae of a Myxomycete in forming the plasmodium 



