44 American Quarterly Microscopical Journal. 



wards until they meet. On meeting, the tips of these outgrowths will 

 be absorbed, and the two cells will thus communicate by means of this 

 newly-formed canal, whereupon it will follow that the contents of both 

 cells will each go half way to meet the other, and their conjoining 

 will take place in the newly-formed canal, or sometimes in one of the 

 cells ; or that the whole of the contents of one of the cells will pass 

 over and combine themselves with the contents of the other. In either 

 case the result will be the formation of a new body — well known as 

 the zygospore, but also known under many other denominations. But, 

 again, in other forms (Mesocarpus), while the initial process will be the 

 same, so far as the formation of the cross channel goes, the further 

 steps differ much, it being only the green-colored portions of the pro- 

 toplasm of both cells that move over into the canal, whereupon the 

 central portion of this green mass, composed of about equal parts of 

 the contents of the two cells becomes developed into a zygospore, 

 leaving the rest of the cell-contents to fade away. The physiological 

 import of these two quite dififerent phenomena was therefore this : in 

 Zygnema and its allies the total contents of two of the cells were re- 

 quired to form a zygospore— whereas in Mesocarpus this was formed 

 out of only portions of the cell-contents. There is thus no strict 

 analogy between these two forms of zygospores, and they probably 

 should not both receive the same name. De Bary perceiving this, 

 referred to the one as resting-spores formed by the partition of the 

 zygospore (the parts destitute of green contents having been parti- 

 tioned off), strangely applying this term to that stage when the two 

 cells had combined to form one, and to the other as resting-spores 

 without partition. De Bary's attempt at being logical has apparently 

 been overlooked by many writers on this subject, notably by such 

 eminent investigators as Max Cornu and Sachs, who still apply the 

 term zygospore to both forms, but Pringsheim has grappled with the 

 difficulty in his most thoughtful paper " On the Alternation of Genera- 

 tion in Thallophytes," and suggests that the first stage in the repro- 

 ductive proscess in Mesocarpus is the "conjugation" stage — here the 

 cells join and become, so far as their cell-walls are concerned, united 

 into one. The next stage is the more important one, in which the cell- 

 contents commingle, and the result is the production of the central cell 

 — a carpospore — and of two or four cells which surround it, and form 

 the equivalent of a fruit-like body, or sporocarp, and of course it 

 would make no matter whether this sporocarp were formed in the con- 

 necting canal as in Mesocarpus, or whether it fills this and extends 

 over into both the cells as in Staurospermum, or as in Plagiospermum 

 is altogether formed in one of the cells ; the essential feature being the 

 differentiation into the carpospore and its investing covering the spor- 

 ocarp. 



Now Dr. Wittrock has made the rather startling observation that in 



