44 



OEGANOGBAPHY. 



Fig. 88. 



Fig. 88. 

 Vessel 

 sliowiii? 

 aconibi- 

 iiatioti of 

 spiral 

 and reti- 

 culated 

 fibres, 

 and sca- 

 lariforni 

 mark- 

 ings. 



monly tapering points like the true spiral vessels, and thus over- 

 lap at their extremities when they come in contact {fig. 86), in 

 which case they appear to be nothing more than elongated tubular 

 cells. In some other instances they terminate more or less 

 obliquely, or by flattened ends, as if formed of rows of cells like 

 most pitted vessels, and that this is their real 

 origin in such cases is proved also by the oc- 

 currence occasionally of contractions on the 

 sides of their walls, so that they assume a 

 beaded appearance, such contractions indica- 

 ting the points where the component cells 

 come in contact {figs. 82 and 87). In rare 

 instances the true spiral vessels also present 

 similar contractions on their walls. 



These vessels are but slight modifications 

 of the true spiral. This is proved by the fact 

 that we frequently find in the same vessel 

 one or more of the above forms combined 

 with the spiral {figs. 84 and 88), and thus 

 forming intermediate states of each other. 

 According to Schleiden and others, they are not only slight mo- 

 difications of spiral vessels, but are actually produced from them 

 in consequence of certain alterations which take place in the 

 course of their development. Thus, annular vessels according to 

 this view, are formed by the growing together of portions of the 

 original spiral fibre into rings, the intermediate portions between 

 such rings becoming ultimately absorbed. Keticulated and 

 scalariform vessels again, are said to be formed by the for- 

 mation of cross fibres in various directions between the coils of 

 the spiral fibre, so that the spiral is converted into a reticulated 

 or scalariform vessel. Other observers, especially Mohl, state 

 positively that there is no change produced in the condition of the 

 fibre within these vessels by age, but that it is always deposited 

 originally in the same condition which it ultimately assumes, 

 and that the seeming transitional stages from spiral vessels 

 into anmilar and reticulated, are permanent intermediate forms 

 between them. 



f. Laticiferous Vessels or Tissue. — These constitute the MilJc- 

 vessels of the old authors. They consist of long branched tubes 

 or passages, lying in no definite position with regard to the 

 other tissues {figs. 89 and 90), and anastomosing or uniting 

 freely with each other like the veins of animals, from which 

 peculiarity they maybe at once distinguished from other vessels. 

 When first formed these vessels are exceedingly minute and 

 their walls are very thin, but they become large and thick-sided 

 as they increase in age, but even then rarely present any pits or 

 spiral deposits in their interior, as is the case in the thickened 

 cells and vessels already described. A common size is the yioo 



