414 SYSTEMATIC BOTANY. 



manner. The gonidia (algae) must be looked upon as independent 

 organisms, imprisoned and forced to serve the double purpose of 

 providing for themselves and their parasites. At the same time 

 they reproduce their own species. Their specific identity with 

 members of the genera Pleurococcus, Nostoc, &c. is well established. 

 The parasites, on the other hand, are true ascomycetous Fungi, 

 reproducing themselves in a strictly ascomycetous manner, and, 

 instead of living on tissues which sooner or later succumb to their 

 demands, have selected hosts offering the greater advantage of 

 persistent life. Of the two components the Fungus is the superior 

 both in bulk and nature, and it is for this reason that the Lichens 

 must be classed as Ascomycetes. 



ALGLX. By excluding Lichens, as a Family, the division of the 

 Thallophyta is reduced to that of Fungi and Algae. The Algae 

 may be said to form a parallel Family to the Fungi. The same 

 gradation from members which consist of a single cell to higher 

 forms, the thallus of which possesses a structure of a more com- 

 plicated nature, exists, and the morphological characters rising with 

 equal step present strong marks of similarity with the parallel 

 Family. It has been said that Algae are Thallophytes containing 

 chlorophyll, and Fungi are Thallophytes in which it is absent ; but 

 this classification is arbitrary and otherwise objectionable as based 

 on subjective characters. 



The thallus of the higher Algae resembles that of the higher 

 Fungi. Its histological peculiarities are not markedly different 

 from those of the Fungi. It consists usually of pseudo-parenchyme ; 

 and in some instances a seeming differentiation of tissue into epi- 

 dermis and fundamental tissue is exhibited, though the so-called 

 epidermis must be regarded as only analogous to true epidermis. 

 The cell-walls consist of an unlignified cellulose, which shows a 

 blue colour on the application of iodine and sulphuric acid. Many 

 Algae are enveloped in a gelatinous substance, which is produced 

 by a process of degradation of the cell- wall. Others again, owing 

 to the deposition of calcium carbonate in the cell- wall or its excre- 

 tion into the intercellular spaces, attain a calcareous structure, as 

 in Corallina. The gelatinous substance serves as a means of fixing 

 the plant to its station, and the calcareous or silicate coats form a 

 valuable protection. It has been stated that the cells possess a 

 nucleus ; but this is not well established. Starch occurs frequently, 

 and chlorophyll, sometimes covered by pigments of various colours 

 (which can easily be removed by cold distilled water), is constantly 

 present. The algal cell, from 'the possession of these substances, 

 stands individually much nearer the ideal perfect vegetable cell 

 than the fungal cell ; and the reason is apparent ; for, whereas the 



