THK PLANT WORI^D 233 



and ( — ) strains of a heterothallic kind, the homothallic kind will attempt 

 zygosporic reproduction with both ( + ) and ( — ) strain plants, from which 

 the bisexual nature of the homothallic form is inferred. 



The general fact of the existence of two strains is beautifully demon- 

 strated by Blakeslee by planting, on the surface of an agriculture medium, 

 spores from previously determined strains in such a manner that, if the 

 view be correct, the contiguous lines of the different mycelia will form a 

 geometrical figure, the lines of which will be studded with zygospores or not 

 according to the strains in juxtaposition. The paper is accompanied by 

 photographs, showing such geometrical figures of surprising regularity. 



The conclusion of this matter, in a word, is the majority of the 

 Mucoraceae are sexually differentiated, but that the difference is one not 

 evident structurally but physiologically. The minority, on the other 

 hand, are hermaphrodite. 



A few points remain to be mentioned. Blakeslee shows that certain 

 races exist among the heterothallic forms which do not respond to (+) 

 and ( — ) strains, which are known to occur in the .same species. It is 

 also known that in Mucor vuicedo, the power of conjugation may be lost 

 by cultivation under unfavorable conditions. Thus, there may arise a 

 " neutral " strain. 



In regard to the process of conjugation it is pointed out that the 

 descriptions usually given in the text books are incorrect in representing 

 i^is. pro gametes (the gametes of descriptions) as arising on neighboring 

 hyphae, and as approaching and finally uniting. The truth is that the 

 progametes arise when hyphae, capable of forming them, touch each 

 other; and they always remain in contact, but, by their growth, force 

 the hyphae apart. 



Differences in the size and form of the conjugating tubes or progametes 

 are inconstant, and are not correlated wilh the sexual differences, which 

 are purely physiological. 



COVER YOUR INDOOR PLANTS WITH GLASS. 



Many teachers and others who have tried to cultivate plants in the 

 school-room have suffered disappointment from time to time from the 

 failure of the plants to cope with the very dry atmosphere of indoors, 

 especially when steam heat is used. The dryness of this atmosphere is 

 much greater than that of a desert, and so failure is to be expected, especi- 

 ally in the case of delicate things such as many ferns. The writer when 

 a child built, with his father's help, a window conservatory a yard square, 

 in which a rock-work was arranged with a miniature waterfall and pond, 

 so as to get a landscape effect. In the water pollywogs, small fish and 



