BIOLOGY AND LIFE filSTOBY. 



13 



Fig. 1.— A seed of mistletoe pasted on a branch by berry 

 pulp and ready to germinate: a. Beak of seed coat; b. 

 fibrous coat of seed: c. root tip of embryo: d. d. berry 

 pulp: 'e. e. lenticels on branch. (All very much enlarged.) 



They begin to be distributed upon branches in December and Janu- 

 ary, but favorable conditions for germination are not likely to occur 

 before March, and perhaps not before April or May, depending 

 upon the temperature, and when this is sufficiently high upon the 

 appearance of a period of rainy, humid weather. Whether the seeds 

 placed upon branches in midwinter remain capable of germination 

 as late as April or May is not known, but of course many berries 

 remain to be distributed as 

 late as May. If it be true 

 that birds eat mistletoe ber- 

 ries only when other choicer 

 kinds are no longer avail- 

 able, then the chief season 

 of distribution would about 

 coincide with the more fa- 

 vorable conditions for ger- 

 mination. 



The pulpy covering in 

 which seeds are embedded 

 upon a branch is a protection to them against extreme drying out and 

 doubtless useful also in absorbing water before germination, thus allow- 

 ing the seed to lie in a moist, slimy matrix. (See fig. 1.) The seed 

 structure proper is also adapted to the arid conditions upon a branch. 

 The seed is invested in a fibrous coat (endocarp) quite unlike the cus- 

 tomary hard shell of berry seeds, which is peculiarly active in absorb- 

 ing water and transmitting it to the living parts within. The peculiar 

 thickening of the walls of the cells in this fibrous coat suggests the 



water-absorbing tracheid cells 

 of sphagnum moss and of the 

 d velamen in the air roots of 

 certain orchids, both of which 

 types are noteworthy because 

 of their water-absorbing prop- 

 erties. 



Within the fibrous coat lies 

 a body of food material or 

 endosperm in which the mi- 

 nute embryo lies embedded, except for its slightly protruding 

 root tip (fig. 2). Both embryo and endosperm retain chlorophyll 

 pigment throughout the dormant period, but previous to germi- 

 nation the green color becomes intensified and the presence of a 

 gas (oxygen?) in the interspaces shows that the seed is already 

 a carbon-assimilating body, able to proceed with its development 

 within the moment of arrival of favorable conditions or of lying 

 dormant and uninjured with the return of arid conditions. It 



160 



Fig. 2. — Sectional view of a germinating mistletoe seed: 

 a. Embryo, showing knob-like enlargement of root 

 end; 6. cotyledons of embryo: c. endosperm or food 

 supply: d, fibrous seed coat. 



