It is also found in small quantities in sea-water, in some seaweeds, and in various mineral and medicinal springs.
The ash of seaweeds, known in Scotland as kelp, and in Brittany as varec, was formerly used as a source of iodine to a greater extent than is at present the case.
None of the existing Red Seaweeds (Rhodophyceae) has a unicellular body.
Some bulky Brown Seaweeds, where assimilation is strongly localized, some of the deep cells are highly specialized for the latter function.
The group, the exceptions being met with almost entirely among the higher Brown Seaweeds, in which is found parenchyma produced by the segmentation of an apical cell of the whole shoot, or by cell division in some other type of meristem.