264 GROWTH AND ORIGIN OF MULTICELLULAR PLANTS. 
— of Sachs* in this matter. In the above genera all the cells 
not transformed into hormogonia; but a few remain at the 
tae of the sheath, the uppermost of which acts as a new growing- 
point, and by cell-divis vision gives origin to a second string of cells 
and ‘Thuret in Calothrix eruginea ., and an indefinite num- 
ber in ca plana Thur. 
The peculiar secondary devel opment of cells described above is 
evidently. due to the power possessed by t the uppermost cell of those 
sie ig at the base of the sheath, in virtue of its undifferentiated 
ante 
originally a transverse sept yielding to the 
pressure of the increasing volume of protoplasm, and thu ti- 
tuting a gro from which cells are cut off by transverse 
deseribed, of i Ni rising a rele te eset sits a still plastic 
$ ranch. pricniket describes a sim 
development as follows: —‘Very frequently, however, after the 
evacuatio: Be otber- ou: its supporting cell grows 
creasing in length, aeeiciee n in imilar er. The next 
change consists in tion of the protoplasm at the distal 
ae of each cell, inn sae by the appearance of a thickening of the 
wall in the form of a ring projecti ing into the cell. The ring is at 
* «Text-book of Botany,’ English ed. p + Loe. cit. pl. xi. & xxxvi. 
} Prof. F. Schmitz, ‘On the a. os the Floridee.’ Transl. in Ann. 
& Mag. Nat. Hist., Jan. 1884. oe 
