MacMillax : Observations ox Nereocvstis . 283 



r 



cover that the growth in thickness is definitely terminated except 

 by the cold of the autumn, when the growth of the whole plant 

 ceases and later the individual perishes. 



Fixation of the Haptcrc, — If the end of an hapteric branch 

 comes In contact with the surface of a rock or other object which 

 gives the necessar}^ resistance, a fixation-area is developed. The 

 epidermal cells of the tip lose their chromatophores and the layers 

 just within remain small but thicken their walls. ' The erencrat 

 shape of the cell-cavities throughout the fixation-area remains very 

 similar to that of the cambial cells from which they were developed. 



1 1 



Growth in length is now terminated, but growth in thickness con- 

 tinues. Sometimes one haptcre affixes itself to a neighboring 

 haptere, in which case the ordinary fixation-area arises precisely as 

 if the organ had been affixed to a rock, but this obviously cannot 

 be a common occurrence ; yet in every holdfast that is fully de- 



I 



velopcd several such fixations of one haptere to another are likely 

 to be met with. 



Callosities of the Stipe— Hh^ characteristic verrucose confluent 

 or elongated callosities of the stipe originate from emergences 

 precisely similar to those which in the holdfast region produce the 

 hapteric branches. I have not observed dichotomy in these cal- 

 losities, nor do their surfaces become modified into definite fixation^ 



I ' 



areas. Where two long stipes of adjacent plants have become en- 

 twined as frequently happens, the callosities are well developed 

 all along the area of contact. Their structure is eiltogether 

 equivalent to that of the hapteric branches, and as previously 

 noted, I consider them homologous with hapteres. They may be 

 regarded as cushions to prevent abrasion when two or more stipes 

 have become intertwined. 



I 



Structure of the mature Flaptere, — When full-grown the haptere 

 consists of but four readily distinguishable tissue areas, the epi- 

 dermis, the lateral cambium, the rather thick-wallcd fundamentalj 

 tissue, and the fixation-area. Chromatophores are not so abund- 

 ant nor deeply stained in the epidermis as in the same layer of the 



I 



pneumatocyst or laminae, hence the hapteric region is of a much 

 lighter green than the portions of the plant exposed to stronger 



I 



illumination. The same is true of the epidermal region on the 

 lower portion of the stipe. The cambial area in the mature hap- 



