Lecture XV. 115 



Polysiphonia from its base out to its end, we find that it bears 

 two kinds of lateral shoots. The first are just like the main 

 axis possessing a cortex and a chain of axial cells ; the second 

 are filamentous, being a single row of cells tapering to a point, 

 and supporting a few similar filamentous branches. The name 

 branches may be reserved more properly for the former; the 

 latter are described as hairs. The extreme end of a branch is 

 rounded, being occupied by a small hemispherical cell. Im- 

 mediately next to this and below it are found several disc- 

 shaped cells. These have arisen as segments cut off from the 

 base of the hemispherical cell, and each gives rise to the cells 

 of one whole segment of the stem. At a short distance back 

 from this short apical cell longitudinal divisions are formed in 

 the disc-shaped cells cutting off the cortical cells from the axial 

 cell. The first division which is formed partitioning the dis- 

 coid cells from the apical cell is not absolutely complete, but 

 the transverse wall is left perforated by an exceedingly minute 

 pore, through which a fine thread of protoplasm passes con- 

 necting the discoid cell with the apical cell. When the next 

 segment is cut off a similar protoplasmic connection is formed. 

 Hence the whole series of axial cells in a branch are connected 

 by these fine protoplasmic strands. They may be often clearly 

 seen by focussing deep into the branch. In the same way the 

 partitions of cellulose separating the cortical cells from the 

 axial cell are perforated and protoplasmic connections are left 

 binding the cortical and axial cells of a segment. It is evident 

 that this method of development cannot provide protoplasmic 

 connections between the cortical cells of adjacent segments. 

 But such connections are to be found in the older" parts of 

 the branch. They are produced in a very peculiar manner. 

 The nucleus of a cortical cell moves towards one end and 

 there divides in two. One of the nuclei thus formed moves 

 still closer to the end and becomes separated off into a very 

 small cell. The partition wall, however, is perforated, and so 

 the cytoplasm of the cortical cell and its tiny fragment are con- 

 tinuous. The cytoplasm of the fragment now grows out towards 

 the nearest cortical cell of the adjacent segment, dissolving its 

 way through the barrier of cellulose. When the channel is 

 complete and connection is made with the cytoplasm of the 

 cortical cell of the neighbouring segment the nucleus of the 

 fragment passes through the channel and enters the adjacent 

 cortical cell. The fragment now shrinks in size and only a 

 fine thread of protoplasm, with a slight enlargement upon it, 



