12 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



gonia and by spores. Both modes, however, are entirely of a non-sexual 

 character. In the genera with numerous heterocysts, as No&toc, the hor- 

 mogonia are formed as follows : The cells intermediate between two hete- 

 rocysts escape in the form of a small chain, called a hormogonium, and swim 

 about with a spiral motion through the water. They at length become 

 quiescent and begin to divide both transversely and longitudinally. Of 

 the cells thus formed some become heterocysts, and in process of time a new 

 Nostoc is formed. In the species destitute of heterocysts, or in which the 

 heterocysts are few in number, the hormogonia are formed in a different 

 manner. At certain points in the sheath of the trichoma constrictions 

 are formed, and the cells between the constriction adhere to one another 

 to form a hormogonium. We thus have formed a necklace of hormo- 

 gonia, which are capable of moving upwards and downwards in the 

 sheath until finally it is ruptured and the hormogonia make their escape. 

 When free they are capable of moving about to a slight degree in the 

 water, and eventually come to rest, and new heterocysts and trichomata 

 are then formed by cell division. 



The so-called spores of the Nostochinecc are formed by the enlargement 

 of some of the ordinary cells to several times their original length until 

 they become ovoid or cylindrical (PI. I, fig. 3, b). They are found in a num- 

 ber of genera but in a number of others they have not yet been observed. 

 They usually occupy a fixed position with regard to the heterocyst, so that 

 they are used as a generic mark. When ripe they have a dense outer 

 covering and become at times quite dark colored. They are more resist- 

 ant than the ordinary cells and do not usually germinate until after a 

 period of rest. In germination, which has only been observed in a few 

 instances, the outer wall of the spore bursts open and the contents grow 

 out iu the form of a filament, in which by transverse division the ordi- 

 nary cells are formed. 



The Oryptophycece are algae which flourish only in summer, but which 

 can be found to some extent at all seasons. Most of them form slimy 

 expansions on mud, wharves, stones, and on dead algae. They are not 

 often found submerged at any depth, but are most abundant near high- 

 water mark. A few filamentous species attain a length of some inches 

 but only one, Lyngbya majmcula, is sufficiently striking to have gained 

 a popular name — mermaid's hair. The species of Oscillaria, Spintlina, 

 and Beggiatoa, are capable of oscillating rapidly, but in this respect 

 The marine species are not so well marked as the species of fresh water. 

 The Beggiatocc which are found on putrefying algse give off the dis- 

 agreeable odor of sulphuretted hydrogen often noticed at the sea-shore 

 in hot weather. The species of Cryptophyceai are very widely diffused, 

 and, with two exceptions, our forms are all common in Europe. 



Zoospores — This order includes not only the greater part of the 

 Chlorospermccc of Harvey's Nereis, with the exception of the OaciUatoria- 

 cew, which belong to the Gryptophycew, but also the Laminariacece and all 

 the Dietyotacecv which Harvey attributes to the New England coast. Al- 



