BiHD. — Lianes of the Ancient Forest of Canterhicry Plains. 351 



The development of large intercellular spaces is more connected with 

 transpiration. Cowles (1911, p. 554) states that it is highly probable that 

 the feature is caused by the small transpiration Avhich characterizes such 

 damp shaded regions. But at the same time it cannot be doubted that the 

 spaces are of great advantage to the plant. They necessarily result in an 

 increase in leaf-size, and at the same time, although the transpiration-rate 

 is low, the intercellular spaces ensure an efficient aeration of the photo- 

 synthetic tissues. This view of the development of intercellular spaces 

 explains their absence— or, rather, reduction — in the exposed sun leaves, 

 which it is obvious must also have tissues aerated. The aeration is here 

 aided by the greater transpiration-current, due to the dryness and warmth 

 of the surrounding atmosphere; for, though transpiration may result in 

 partial closure of the stomata, Cowles states that at the same time the 

 increase of transpiration may cause an increase in the number of stomata. 

 This view is in accord with the increase noted in all the liane sun leaves. 

 It is further remarked by Cowles, " Stomatal structures and activities 

 cannot stop transpiration ; at best there is only retardation " (p. 567). 

 Now, if this be correct, then the larger number of stomata on the leaves 

 in the sunlight will, by increasing the transpiration-rate, be of advantage 

 to the liane in aiding the conduction of water, with its contained salts, 

 through the vessels of the stem. And it is obvious that this conduction in 

 so small a stem to so great a height is for the liane a matter of supreme 

 importance. 



The great development of cuticle in the open has also been interpreted 

 as due to increased transpiration. A\1iile the loss in external transpiration 

 due to cuticularization may be fully balanced by the gain caused by 

 the increased number of stomata, the cuticle serves an important role in 

 strengthening the leaf, and therefore ensuring protection from wind and 

 storms. 



The cells of the epidermis can be roughly classed into four types : Type 1, 

 walls of cells very wavy [e.g., Fuchsia Colensoi, shade leaf) ; type 2, 

 walls wavy, but to a far less extent than in type 1 {e.g., Rubus cissoides, 

 shade leaf) ; type 3, walls straighter than in type 2, but not so straight 

 as in type 4 {e.g., Clematis indivisa, shade leaf) ; type 4, walls straight, 

 and perhaps slightlv rounded at the corners {e.g.. Clematis indivisa, sun 

 leaf). 



The importance of variation in the regularity of the lateral walls of 

 epidermal cells is not so evident ; but since they are more wavy in the 

 lower epidermis than in the upper, and more regular in sun leaver than 

 in shade leaves, it is probable that transpiration is a factor determining 

 their regularity. 



Finally, we must notice how the structure of the stem must be related 

 to all questions dealing with water-conduction and transpiration. In lianes 

 especially do the stems have to be particularly adapted for rapid water- 

 carriage, and without knowledge of these adaptations no comprehensive 

 conclusions can be obtained. 



